How to wire break on rise timer switch to pressuretrol?

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?

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.

> @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.