How to wire break on rise timer switch to pressuretrol?

Motorapido

My new break-on-rise timer switch has a terminal marked Line and a terminal marked LOAD. As I face my pressuretrol with the cover plate removed, the switch mechanism in the pressuretrol, which looks like a caramel colored seesaw, has a terminal and wire on the high/right side of the seesaw and a terminal and wire on the low/left side of the seesaw. I assume that I wire the LINE lead from the timer switch to the right-hand, higher-sitting terminal on the pressuretrol seesaw switch, after removing the wire that is currently connected there, and then take that wire that I just disconnected from the high-side/right-side terminal and connect it to the LOAD wire on the timer. Do I have this right? It appears that the wire going to the left/low side of the seesaw switch comes off the 24v transformer inside the boiler enclosure, and that the wire coming off the right/high-side of the seessaw switch on the pressuretrol continues on to the LWCO. Please educate me on this (I'm doing this to add a 5 minute delay after cycling on pressure (19 ounces, with my recalibrated pressuretrol) to allow the radiators to continue condensing steam and putting out heat, to satisfy the termostat before running another firing cycle. I want to make sure I wire it right.

Motorapido

I should note that I will soon be upgrading to a vaporstat, but for now I want to use the timer switch with the existing pressuretrol. Also, after I get the vaporstat, I will keep the pressuretrol in place just as an extra safety control in case the vaporstat fails and does not shut the boiler down on pressure.

Jamie Hall

That wiring -- so far as it concerns the pressuretrol and the contacts in the timer -- sounds right. However, I would ask -- what is the power supply for the timer itself? Or is it clockwork?

Motorapido

My pressuretrol operates on 24v. The timer has just two leads, one for line and one for load. No neutral or ground. Here is a link to the timer https://www.amazon.com/gp/product/B01LYA0LJX/ref=pe_344980_264654940_em_1p_2_ti

I'm no electronics wiz by a long shot, but it is hard for me to conceive of a device that takes only a hot lead and does not require a neutral or ground.

Motorapido

While I'm at it, what type of box would I use to contain this timer switch? It has one hole through the center of the switch unit. I could do an ugly job and just zip tie it to the pressuretrol body, but I'd like to make it look completely pro. Suggestions?

EBEBRATT-Ed

I hope you understand where I'm coming from.

Unless you totally understand what you are doing you shouldn't be fooling with a pressure control which is a boiler safety device.

That's why people in this business have licenses. While I am not against homeowners working on their own equipment you need to completely understand what you are doing. Your questions show that you do not

Jamie Hall

Keep in mind that you are installing this in the safety circuits on your boiler.

There are two things which concern me. First, it appears that it is intended to keep an internal set of contacts -- probably solid state -- open for a period of time after voltage is applied to the two load terminals, and then close. I don't quite see how this unit will function to hold off a reclose after the load -- your safety circuits -- is opened. It may work, however, to hold off a reclose after your safety circuits -- in most cases the pressuretrol -- recloses. Which brings up the second concern: how much current/voltage does it allow to pass while the delay is in progress? Probably not enough to start a burner, but... it doesn't say.

And what happens if the thermostat opens while it is in progress?

Then a third thought: this thing is rated at 1.5 amps. What does your circuit draw? Starting current? Running? It will have to be fused for that 1.5 amp rating.

Perhaps I am unduly skeptical. I continue to think that a properly set up thermostat will do exactly the same job -- if preventing overshoot is your aim -- much more simply. If increased efficiency is the object, keep in mind one simple relationship: the heat required to keep the structure at the desired temperature must come from the combustion of fuel in the boiler. There is no other source. So the timer arrangement will not reduce the required burner on time -- although it may spread it out. Indeed, there are theoretical reasons to suppose that it will increase the burner on time, as some fuel will be required to bring the boiler back up to temperature after the longer off delay forced by the timer.

Chris_L

Yes, I have to wonder if this device is what you really want, even if you can get it to work. Here is some more information: http://www.icmcontrols.com/ProdImages/ICM102-ag.pdf

Looks to me like this will give you a delay on each call for heat, not just a delay after you get a pressuretrol (or vaportrol) cut-out.

Jamie Hall

Chris_L said:

Yes, I have to wonder if this device is what you really want, even if you can get it to work. Here is some more information: http://www.icmcontrols.com/ProdImages/ICM102-ag.pdf

Looks to me like this will give you a delay on each call for heat, not just a delay after you get a pressuretrol (or vaportrol) cut-out.

I think you're right on that, @Chris_L . And I might add further -- any delay which it inserts will be after the pressuretrol or vapourstat recloses...

Motorapido

EBEBRATT-Ed said:

I hope you understand where I'm coming from.

Unless you totally understand what you are doing you shouldn't be fooling with a pressure control which is a boiler safety device.

That's why people in this business have licenses. While I am not against homeowners working on their own equipment you need to completely understand what you are doing. Your questions show that you do not

EBEBRATT -- I understand and appreciate your comments. And that is why I am studying and planning carefully in advance, so I am not just tinkering. I have extensive mechanical experience in many areas -- vintage motorcycle restoration, including all engine and electrical work, thorough metal shop skills, general construction and home wiring. In my upcoming enhancements to my system, I will be running both a pressuretrol and vaporstat, so that I will have two safety controls instead of one. I appreciate and respect the need for thorough knowledge and appropriate methodology.

In my proposed application of this timer, it seems to me that putting the timer after the pressuretrol is the right approach for what I am trying to achieve. Despite having 6 Big Mouths (3 each at the ends of my two mains), which gives me maximum main venting, I still cycle on pressure, and with the pressuretrol calibrated downward, I build to about 19 ounces of pressure before the system cycles on pressure one to three times if it is pretty cold outside. My radiators all have new Maid-O-Mist vents on them, and I have adjusted orifice sizes to achieve consistent, event heating. The radiators heat pretty even all across when it is cold.
The theory that makes sense to me is that if I delay the restart after each shut-down on pressure, I am allowing the remaining steam in the mains to continue to reach the radiators and condense in the radiators, which will continue to increase the room temperature during this delayed re-start. With thoroughly insulated mains, the time it takes upon restart to create new steam is minimal. During that shut-down time, my automatic damper is retaining heat in the boiler room and minimizing loss up the chimney. I am not trying to prevent overshoots, since I don't experience troublesome overshoots. I'm just seeking to delay the restart maybe 3 to 5 minutes, so that I continue to extract heat from the steam already created before the system restarts and begins to build pressure again.
I figured I'd go down this road rather than hire somebody to downfire the existing burner or to install a two-stage burner. I have read many statements indicating that downfiring and retrofitting two-stage burners both come with potential risks and drawbacks.
EBEBRATT -- I do appreciate your comments and I accept them and understand them in the manner that you intended them.

Jamie Hall

As I said before, elementary thermodynamics 101: the only heat source for your building is the fuel burned by the boiler. Period. You will NOT save any fuel by delaying the restart on pressure. Sorry. There is no free lunch.

Motorapido

Jamie Hall said:

As I said before, elementary thermodynamics 101: the only heat source for your building is the fuel burned by the boiler. Period. You will NOT save any fuel by delaying the restart on pressure. Sorry. There is no free lunch.

I see the point. However, by switching to a Vaportat and lowering my cycle-on-pressure cut out to, let's say, 8 or 10 ounces of pressure, down from the current 19 ounces, I will be subtracting the time that the burner currently runs to build to 19 ounces. The higher pressure is not making my radiators put heat into the house faster. It's just wasting gas. During a timer-off delay before the next cycle, the steam I have already created can continue to condense in the radiators, releasing heat while the burner is temporarily off before the timer allows it to turn back on. I view the time spent building pressure beyond 8 to 10 ounces as wasted burning time, and the time off periods as time when the steam I've already created can continue doing its job in the radiators.

Fred

I see where you are trying to go but it actually sounds like your boiler must be way over-sized for the connected radiation. I think what you are going to find, after you install the timer and the vaporstat is that by reducing the cut-out pressure by half of what it is now, you will likely reach cut-out almost twice as fast as you currently do and the timer will be on/off much more frequently that your current set up (maybe not twice as much, with the delay but). I suspect that your Big Mouths will open in that 3 to 5 minute delay (Mine seem to open relatively quickly) and you won't see much "burner off steam benefit" I'm guessing the mass of the already hot radiators gives you about all the after burn benefit you're going to get anyway. JMHO. Having said that, if you are using a deep set-back, stop or reduce that. I do believe that if you can have a two stage gas valve installed and run it on a low burn, after a high fire to get everything steam hot and maybe 3 or 4 ounces of pressure that that is a much better long term solution and certainly will have much less wear and tear on all the switches (timer, damper, Pressuretrol, vaporstat, gas valve, etc. Let the thermostat manage the house temp and use the Vaporstat to manage high/low fire, with a two stage gas valve. If properly installed and a good combustion analysis done at both high and low fire, there is little to no downside and it will probably also save some fuel cost (even though that's not your primary objective here).

PMJ

The farther the system runs up the pressure the higher the overshoot will be. The net heat loss that has to be replaced is determined by the temp difference inside to outside. Overshooting raises this average difference and therefore the fuel consumption for any given desired setpoint. Is it a dramatic amount? No.

The main reason to continue down the road you are on @Motorapido is to even out your heat. You are absolutely correct in that you have identified that when you have hit your first pressure stop you have certainly already produced more steam than is required for the conditions and want to just wait a while to let that heat get into the rooms before firing again.

Is any of this worth any complication of the control at all? Many here say no and I say that is an entirely reasonable position. I also say that the shorter the time is from a call for heat to when the call is satisfied, the less even the heat is. For those who do wish to lengthen this time and get more even heat, timed cycle control is a pretty simple way.

Motorapido

Fred said:

I see where you are trying to go but it actually sounds like your boiler must be way over-sized for the connected radiation. I think what you are going to find, after you install the timer and the vaporstat is that by reducing the cut-out pressure by half of what it is now, you will likely reach cut-out almost twice as fast as you currently do and the timer will be on/off much more frequently that your current set up (maybe not twice as much, with the delay but). I suspect that your Big Mouths will open in that 3 to 5 minute delay (Mine seem to open relatively quickly) and you won't see much "burner off steam benefit" I'm guessing the mass of the already hot radiators gives you about all the after burn benefit you're going to get anyway. JMHO. Having said that, if you are using a deep set-back, stop or reduce that. I do believe that if you can have a two stage gas valve installed and run it on a low burn, after a high fire to get everything steam hot and maybe 3 or 4 ounces of pressure that that is a much better long term solution and certainly will have much less wear and tear on all the switches (timer, damper, Pressuretrol, vaporstat, gas valve, etc. Let the thermostat manage the house temp and use the Vaporstat to manage high/low fire, with a two stage gas valve. If properly installed and a good combustion analysis done at both high and low fire, there is little to no downside and it will probably also save some fuel cost (even though that's not your primary objective here).

I'm about 45 percent oversized, as I recall from my calculations last season. I do not do any thermostat setback, and keep it set at 70 24/7. I would keep it at 66 or so if I lived alone, but The Commander in Chief would prefer 75, so we compromise at a constant 70. I do not experience temperature overshoots for the most part. Generally, a little while after the thermostat stops calling for heat, I will see 71 on the thermostat. That's fine with me. I have not seen a performance change after experimenting with changing the thermostat's cycles per hour from 2 to 4.

I have had no luck in finding a gas expert in the Harrisburg-PA area who is either expert enough to choose and install a two-stage burner for me, or interested in looking into it for me. The Peerless boiler is probably about 10/12 years old, so I assume it is out of warranty, and I don't much worry about the warranty anyway, even if were still in place.

About the issue of wear and tear on components caused by the current short-cycling and how that would be magnified by running a lower pressure cut-out and experiencing even more short cycles -- I wonder if there is any way to ballpark guesstimate the tradeoff between the gas-saving benefit of living with and even increasing short cycling versus the cost of replacing components if they die prematurely from more cycling. Since we can't talk price here or even speculate about price, I have no resource available to me. I do have a hunch, for whatever reason, that the gas savings would outweigh the cost of shortening the lifespan of the burner and controls. But this is just pure gut guessing on my part.

Fred

@Motorapido, I know most gas valve manufacturers and probably Pressuretrol/Vaporstat manufacturers and probably even damper manufacturers can tell you how many cycles they expect from their devices and the mean time between failures. If they are willing to actually give you that information or not, I can't answer. I know, in the past, Barnes and Jones has told us how many cycles they expect from their traps. If you can find that info, you can probably extrapolate a decent estimate of the difference between the "normal" cycling and the anticipated life based on incremental additional cycles per day/month/year.

Jamie Hall

I too see where you are trying to go. But allow me a bit of a dissertation here.

One of the things you mention seeing is a key. You note that the temperature overshoots if you let things run as they are. Back before all this solid state gadgetry, (using the principle place I care for as an example here, since I have extensive records on it), it had a mercury Honeywell T87 thermostat (before that it had a Honeywell bimetal strip thermostat, I forget the model number). That thermostat had a small heater coil in it, called the anticipator. The function of that coil was to add a small amount of extra heat to the thermostat, depending on how long the call lasted, which tricked the thermostat into thinking it was warmer than it really was, and thus turned the thermostat off earlier. Properly adjusted, that small amount of extra heat was just enough to shut off the thermostat just enough too soon to allow the residual heat in the radiators to bring the space temperature up to the set point with no overshoot. Which it did, under most conditions.

The anticipator was finicky, and most average people didn't take the trouble to get it set exactly right for their application. The installer could get it very close (it was marked in amps drawn by the boiler from the thermostat circuit), but not quite. But with care and patience it could be set.

It had an additional curious effect: the thermostat also cooled faster than the space, and so the temperature swing seen by the thermostat was greater than that in the space. The end result was astonishingly even temperatures in the space.

Now. The digital age did away with all that. Instead, we now have cycles per hour. These are based on the premise that some types of heating system heat and cool slowly -- such as steam or gravity hot water -- and some rapidly -- such as hot air. To minimize temperature swing, a system which responds (both up and down) rapidly will need more, but shorter, cycles per hour. A system which responds slowly will need fewer, but longer cycles. The digital thermostat will call off a little before the set point is reached; that length of time is controlled by the cycles per hour (sooner for longer slow cycles, later for short fast cycles) and in some thermostats there is also a memory algorithm which notes the degree of overshoot and adjusts that timing, but only within rather narrow limits.

My apologies for the dissertation, but the bottom line is this: if you are experiencing overshoot on a normal heating call (not from a setback) you need fewer, longer cycles per hour. If the place gets noticeably cool before the thermostat kicks in, you need more, shorter cycles.

Now on the fuel wasted by building pressure. You are correct on that; it is mostly (not entirely) wasted. What is needed, then is to eliminate that. As I indicated in another thread dealing with control theory, ideally to minimise that waste one wants to hold the pressure within a rather narrow range -- that is the range which is correct at the boiler to keep the steam flowing to the radiators at a constant (or reasonably so) rate. This depends on the system. The best way to determine that pressure is to watch a low pressure gauge as the system heats. Generally one will observe that after the burner starts, it will rise to some low level (in the main place I care for, about 3.5 ounces) and just sit there. At some point, in a long call and if the boiler has more steam generating capacity than the radiation has condensing capacity, the pressure will start to rise again. That's when you want the boiler to shut down; to avoid nuisance trips a 100% margin is reasonable, so in the case I mentioned the vapourstat shuts off the burner at 7 ounces. Keep watching that pressure gauge. You will note that the pressure drops very quickly. Again, ideally you would like the burner to come back on before it drops to 0 and the boiler stops steaming from residual heat in the boiler, so that steam will keep being delivered to the radiation. In practice, this may not be possible due to the post purge and pre purge timings on the burner.

The end result, if both the thermostat and the vapourstat are set properly, is smooth continuous delivery of heat -- steam -- to the radiation just long enough so that the residual heat in the radiation brings the space temperature to the set point.

Now if your boiler is significantly oversized -- and I gather from your comments that yours is (and many are) you will get a few pressure cycles at the end of a normal call. One can reduce that by shortening the calls (as I gather you have done by setting the cycles per hour to 4), but at the expense of greater temperature swings in the space.

One can reduce the fuel burn by shutting the burner off at the correct pressure, but letting it come back on as soon as the pressure drops.

What you will accomplish with the timer will also create wider temperature swings in the space. There will be an additional fuel burn to bring the boiler back up to the boil.

You seem concerned about the effect of multiple starts on the components of the burner. If there were a very large number, or if the timing between starts were very small (say so small that the burner motor hadn't even come to a stop) this could be a problem. But again, as I've said before, unless your burner assembly came off the back of a truck from China, everything is designed for many tens of thousands of cycles (the most vulnerable components are the ignition electrodes, which should be replaced yearly in most cases anyway, and the starting capacitor on the motor). In terms of parts longevity, allow me to point out that there is an effect on the boiler itself: the more, and wider, the temperature swings in the boiler are, the sooner it is likely to crack or leak -- which is a reason to keep the off time as short as possible.

EBEBRATT-Ed

Both @Jamie Hall and @Fred are correct and Jamie's control description is excellent. Really, the bottom line is with a 45% oversized boiler their is not a lot of fine tuning you can do.

If the boiler is 45% oversized on a design day just imagine how much oversized it is for the majority of the year when you only need 40%, 50% 60% capacity of a correctly sized boiler.

Motorapido

> @Jamie Hall said:
> I too see where you are trying to go. But allow me a bit of a dissertation here.
>
> One of the things you mention seeing is a key. You note that the temperature overshoots if you let things run as they are. Back before all this solid state gadgetry, (using the principle place I care for as an example here, since I have extensive records on it), it had a mercury Honeywell T87 thermostat (before that it had a Honeywell bimetal strip thermostat, I forget the model number). That thermostat had a small heater coil in it, called the anticipator. The function of that coil was to add a small amount of extra heat to the thermostat, depending on how long the call lasted, which tricked the thermostat into thinking it was warmer than it really was, and thus turned the thermostat off earlier. Properly adjusted, that small amount of extra heat was just enough to shut off the thermostat just enough too soon to allow the residual heat in the radiators to bring the space temperature up to the set point with no overshoot. Which it did, under most conditions.
>
> The anticipator was finicky, and most average people didn't take the trouble to get it set exactly right for their application. The installer could get it very close (it was marked in amps drawn by the boiler from the thermostat circuit), but not quite. But with care and patience it could be set.
>
> It had an additional curious effect: the thermostat also cooled faster than the space, and so the temperature swing seen by the thermostat was greater than that in the space. The end result was astonishingly even temperatures in the space.
>
> Now. The digital age did away with all that. Instead, we now have cycles per hour. These are based on the premise that some types of heating system heat and cool slowly -- such as steam or gravity hot water -- and some rapidly -- such as hot air. To minimize temperature swing, a system which responds (both up and down) rapidly will need more, but shorter, cycles per hour. A system which responds slowly will need fewer, but longer cycles. The digital thermostat will call off a little before the set point is reached; that length of time is controlled by the cycles per hour (sooner for longer slow cycles, later for short fast cycles) and in some thermostats there is also a memory algorithm which notes the degree of overshoot and adjusts that timing, but only within rather narrow limits.
>
> My apologies for the dissertation, but the bottom line is this: if you are experiencing overshoot on a normal heating call (not from a setback) you need fewer, longer cycles per hour. If the place gets noticeably cool before the thermostat kicks in, you need more, shorter cycles.
>
> Now on the fuel wasted by building pressure. You are correct on that; it is mostly (not entirely) wasted. What is needed, then is to eliminate that. As I indicated in another thread dealing with control theory, ideally to minimise that waste one wants to hold the pressure within a rather narrow range -- that is the range which is correct at the boiler to keep the steam flowing to the radiators at a constant (or reasonably so) rate. This depends on the system. The best way to determine that pressure is to watch a low pressure gauge as the system heats. Generally one will observe that after the burner starts, it will rise to some low level (in the main place I care for, about 3.5 ounces) and just sit there. At some point, in a long call and if the boiler has more steam generating capacity than the radiation has condensing capacity, the pressure will start to rise again. That's when you want the boiler to shut down; to avoid nuisance trips a 100% margin is reasonable, so in the case I mentioned the vapourstat shuts off the burner at 7 ounces. Keep watching that pressure gauge. You will note that the pressure drops very quickly. Again, ideally you would like the burner to come back on before it drops to 0 and the boiler stops steaming from residual heat in the boiler, so that steam will keep being delivered to the radiation. In practice, this may not be possible due to the post purge and pre purge timings on the burner.
>
> The end result, if both the thermostat and the vapourstat are set properly, is smooth continuous delivery of heat -- steam -- to the radiation just long enough so that the residual heat in the radiation brings the space temperature to the set point.
>
> Now if your boiler is significantly oversized -- and I gather from your comments that yours is (and many are) you will get a few pressure cycles at the end of a normal call. One can reduce that by shortening the calls (as I gather you have done by setting the cycles per hour to 4), but at the expense of greater temperature swings in the space.
>
> One can reduce the fuel burn by shutting the burner off at the correct pressure, but letting it come back on as soon as the pressure drops.
>
> What you will accomplish with the timer will also create wider temperature swings in the space. There will be an additional fuel burn to bring the boiler back up to the boil.
>
> You seem concerned about the effect of multiple starts on the components of the burner. If there were a very large number, or if the timing between starts were very small (say so small that the burner motor hadn't even come to a stop) this could be a problem. But again, as I've said before, unless your burner assembly came off the back of a truck from China, everything is designed for many tens of thousands of cycles (the most vulnerable components are the ignition electrodes, which should be replaced yearly in most cases anyway, and the starting capacitor on the motor). In terms of parts longevity, allow me to point out that there is an effect on the boiler itself: the more, and wider, the temperature swings in the boiler are, the sooner it is likely to crack or leak -- which is a reason to keep the off time as short as possible.

This is a wonderful, thorough analysis that is altering my thinking. I'm glad the timer was only about $6. I think I'll just l skip installing it, but add the new vaporstat and set it to 8 ounces and start recording data on my cycling at various outdoor temperatures. Now, is reaching 71 degrees when I wanted 70 an overshot of any material concern? If it overshot to 75 or 76, that would be a big deal, but just one degree too high seems pretty dang good. Before the stat calls for heat, I never see a display temperature below 70, so my swing is just 1 degree. I'm fine with that. I never knew the gas igniter should be changed annually. I'll do that now that I know. The two separate technicians I've had for my two fall inspections and cleaning did nothing more than clean the burner tubes and remove the flue pipe to eyeball the chimney. No combustion analysis test, no gas pressure test. They looked at me like I was an idiot for asking them to do that and then said they didn't have the tools. Both were techs from relatively large HVAC businesses. Damn frustrating. I need to find a true pro to do that analysis and to find be a two stage burner and install it properly. It's a shame when you hire a big outfit that doesn't practice their trade as they should.
Thanks for all these thorough, detailed posts. You guys are good cyber friends to me. Beers, my treat, if we ever have the pleasure to meet.

PMJ

Jamie said a lot of things in his post. While I can't go through all of it I will say the following.

Coal fired steam was, if nothing else, very even heat. It was even because it was physically quite impossible to change anything about it quickly. With the two speed fires most common today (high and off) things can and do change very quickly. This means uneven heat.

There is a number of minutes per hour a boiler must run to heat the structure it is in based on its size and the difference between inside and outside temperature. If you do all burns in straight runs until thermostats are satisfied then the off wait times that are required between burns will become maximums. Operating this way( the lowest number of complete cycles per hour) will result in the biggest change in temperature during each fire/wait cycle of both the rads and the rooms. Pressure in any amount will make this worse. Pressure by its very presence proves that more steam is in your radiators than is required for the conditions and causes overshoot of some amount. This amount may be quite tolerable and not worth any discussion to many, but saying that does not mean the overshoot isn't happening. Many of us have shown that heating is quite possible with header pressures that never exceed 1-2 inches of water. We do this by never filling rads enough to make any pressure - because that much fill is never needed.

Anyone wishing to make the heat more even should stay away from pressure in any amount, stay away from long burns, stay away from quickly satisfied calls for heat. Accomplishing these things will require controlling the fire with time in some way. Even one degree swings every cycle became unacceptable to me long ago. A one degree swing on an inside wall containing the thermostat is more than that near an outside wall.

Remember, a "properly" sized boiler is making steam at least at twice the rate needed on an average day. That production simply must be spread out more evenly over time if you really want even heat.

Jamie Hall

Someday I suppose I should write an article on control theory for predictive and reactive control, and open and closed loop systems. It is a fascinating topic and one which, clearly, is rather poorly understood...

But not today.

PMJ

Jamie Hall said:

Someday I suppose I should write an article on control theory for predictive and reactive control, and open and closed loop systems. It is a fascinating topic and one which, clearly, is rather poorly understood...

But not today.

Perhaps you should.

In the end though, any of these control systems that improve our result will end up shortening firings and making them more frequent - just like your anticipator example above which shut the boiler off "early" anticipating the coming heat (shorter burn) and turning it back on sooner anticipating the coming temperature drop (shorter wait). I had one of those and it was pretty good actually. There are different control ways to cause this change but breaking up the run into smaller pieces will always be the result when all there is to work with is high flame and off.

Canucker

Jamie Hall said:

Someday I suppose I should write an article on control theory for predictive and reactive control, and open and closed loop systems. It is a fascinating topic and one which, clearly, is rather poorly understood...

But not today.

Please do @Jamie Hall I would love to read it.

PhilKulkarni

Your two pole delay on make timer uses a triac to switch the load. That causes the output voltage to have a D.C component in it. This in turn causes the gas burner valve to perform erratically when wired in series with the pressuretrol. I therefore use the following timer from Amazon that uses a 10A miniature relay to switch the load:

https://www.amazon.com/gp/product/B00JH1TW8O/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

With this timer I can adjust the delay so the boiler restarts before my Big Mouth main vent opens. It has been working with a 2.5min delay on make for the second season.

Boiler cycling on pressure wastes fuel. My radiators have a large thermal mass and give off heat for some time after the boiler shuts off. The cut off pressure is 2.2PSI. The time delay kicks in at the cut in pressure of 0.6 PSI as measured on a 0-3PSI FS gauge. The boiler stays off at a pressure reading of 0 until the time delay is over.

With my Nest stat I have a negligible temp overshoot, < 1 degree as seen on my Nest app. With the timer I don't see any noticeable overshoot either. I just have fewer cycles to reach my 70 degrees from 66 degrees set back at night.

The timer is fixed to my boiler using velcro and is powered from my 24v Xformer. I can post a picture if it helps.

BobC

I suspect that gas valve is very inductive. Triacs have a problem with that because both sides don't always fire, you casn fix that by over driving the triac but most designers don't know that. Almost all SSR's (solid state relays) use dual SCR's because they are more reliable when it comes to driving very inductive loads.

Bob

Motorapido

PhilKulkarni said:

Your two pole delay on make timer uses a triac to switch the load. That causes the output voltage to have a D.C component in it. This in turn causes the gas burner valve to perform erratically when wired in series with the pressuretrol. I therefore use the following timer from Amazon that uses a 10A miniature relay to switch the load:

https://www.amazon.com/gp/product/B00JH1TW8O/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

With this timer I can adjust the delay so the boiler restarts before my Big Mouth main vent opens. It has been working with a 2.5min delay on make for the second season.

Boiler cycling on pressure wastes fuel. My radiators have a large thermal mass and give off heat for some time after the boiler shuts off. The cut off pressure is 2.2PSI. The time delay kicks in at the cut in pressure of 0.6 PSI as measured on a 0-3PSI FS gauge. The boiler stays off at a pressure reading of 0 until the time delay is over.

With my Nest stat I have a negligible temp overshoot, < 1 degree as seen on my Nest app. With the timer I don't see any noticeable overshoot either. I just have fewer cycles to reach my 70 degrees from 66 degrees set back at night.

The timer is fixed to my boiler using velcro and is powered from my 24v Xformer. I can post a picture if it helps.

PhilKulkarni -- I am reviving this thread. I never installed the timer that I had bought. Can you provide more information on the setup of the timer that you referenced in your message and link? How you wired it, and info on your boiler and system -- one pipe or two? Oversized, I am guessing, since you have applied a timer. I am doing some off-season system cleanup (lwco maintenance, etc) addition of a pressuretrol in series with my existing vaporstate, etc., and now would be a good time to install a timer.