Runaway Pressuretrol...

RobLC · October 2009

I installed a 3psi Wika gauge on a tee with the Honeywell pressuretrol today.

 

Well, the p’trol cuts in with no problem. But it appears this thing has no intention of ever cutting out, ever. It’s entirely up to the thermostat to shut the boiler.

 

I adjusted the differential wheel every way possible and the pressure in the system buries the needle of the 3psi gauge. We were hoping the p’trol would cut out somewhere about 1.5psi or even 2psi. Again, the differential wheel was set to 1 and we even tried 0. Cut in to .05.

 

The p’trol has been cleaned out and we have a brass pigtail now.

 

I was thinking of a Vaporstat but a plumber in a supply house said we can’t use a Vaporstat in a 3 family house - - he said it wouldn’t pass inspection(?)

 

He said, “What do you have, one of those crappy 3” x 3” Honeywell P’trols?”

 

Yes, that’s what we have. 

 

He said, “You need to get the bigger Honeywell P’trol, it’s more accurate.”

 

My questions is: 

 

Should we just replace the P’trol with the same one but new?

Is there a reason why this thing won't cut out?

 

Or should we look into a Vaportstat?

 

If we get a Vaporstat, is the wiring the same?

 

All we have is a red wire and a black wire going to the current P’trol.

Thank you.

 

RobLC

RobLC · October 2009

Apologies folks...

I meant to write:

My questions are:

Alan (California Radiant) Forbes · October 2009

The pressuretrol

is broken. Whatever senses the increase in pressure (a spring?) is not working properly.

I'd get a Vaporstat and set it to operate between 4 and 10 oz. The wiring should be exactly the same, i.e. break on rise.

RobLC · October 2009

Thank you, Alan Forbes...

We'll try to get Vaportstat that breaks on rise.

Operate between 4oz and 10oz.

Is that the range for the cut-in? Or is 4oz the cut-in and 10oz the cut-out?

Our old p'trol was set at .5psi for cut-in and 1.5psi (differential was 1) for cut-out.

We were thinking 8oz for the cut-in and 24oz for the cut-out.

Thank you for taking the time to answer my questions.

RobLC

Alan (California Radiant) Forbes · October 2009

Vaporstat

"Or is 4oz the cut-in and 10oz the cut-out?"

Correct.

RobLC · October 2009

Thanks, Alan...

What are your thoughts on a gas fired boiler that might short cycle because of the lower pressure controlled by the vaporstat?

RobLC

nicholas bonham-carter · October 2009

short-cycling with a vaporstat?

if your main line venting is generous, and your boiler is not over-fired, you should have no short-cycling problems. the vaporstat is so much better at regulating the low pressures that steam thrives on.--nbc

RobLC · October 2009

Thank you, NBC...

Have 2 long mains, one to back of house and one to front. One is 25', the other is 17'. At the end of each main we have a #1 and a #2 Gorton vent on 6" risers. That's 4 vents on the mains. Is that enough? Could we replace the #1's with #2's? That would make 4 #2's. Or is that too much?

I couldn't say if the boiler is overfiring. It hums well and doesn't make noise and the water doesn't surge in sight glass. All the wet returns have been replaced, right up to the boiler.

We live in a three family house. A plumber at a supply house told me that a vaporstat in a three family wouldn't pass inspection. Have you heard of this?

Well, I will look further into the Vaporstat.

Is it safe to run a boiler where the pressuretrol doesn't cut out? I'm thinking yes.

Thank you, NBC, for taking the time to answer my question.

RobLC

nicholas bonham-carter · October 2009

vaporstat+code

i have never heard of any code requirement against the use of a vaporstat, after all, it performs the same function as a p-trol-only better! there is a requirement that the 30 PSI gauge remain, even though for our purposes, it is useless. i have on my pigtail, a 0-15 oz. gauge, the 30 PSI gauge, a vaporstat, and a secondary pressuretrol [set at 3 PSI, in case there is a vaporstat failure]. upstairs, i have a secondary gauge so i can see if the boiler is firing, as it is now so quiet, i can't hear it, [or have i just become more deaf?] before the renovation of our system [55 rads], we could feel the water-hammer through the floor!

as far as the number of main vents on each dry return, my method was to add until silent-no whistling at the rads!

it would not be wise to run a boiler, without a functioning pressuretrol to keep the maximum pressure below its rated maximum.--nbc

Jamie Hall · October 2009

Not particularly

No, it really isn't safe to run a boiler without a functioning pressure cutout. You are counting on either the thermostat turning off at a reasonable time or the pressure relief valve working. And pressuretrols do break, like any other mechanical (or electronic) doodad. Get a nice vapourstat, as has been said, and set it to cutout at about 12 oz with a differential of 8 or so and try it. Then play with it.

You shouldn't really have a problem with the system 'short-cycling' if you don't now, and it does sound as though you have at least adequate venting, if not overly generous. There is a curious thing about 'short-cycling' and cutout pressure with steam: if the venting is even remotely adequate, changing the cutout pressure will make almost no difference in the overall cycle timing. The reason for that is that so long as the radiators are not full of steam (that is, they are still venting air either into the return or through their own vents in one pipe), the pressure in the mains will be very low -- ounces at most, and usually darn near imperceptible, even with a good gauge. Then as soon as that last trap or vent closes -- up the pressure goes. Now the burner will fire until it reaches cutout -- by a minute or several, perhaps -- to reach the higher pressure, but that period of firing does no good to anyone. Once it cuts out, the pressure will drop -- remarkably fast -- and the cycle will repeat. So with a higher cutout, all you are accomplishing is burning fuel, with no heat going anywhere. What you will see with a vapourstat is some savings in fuel, and a somewhat shorter time between when the burner cuts out and when it cuts back in again (this is actually not bad -- it saves the energy required to bring the kettle back up to a boil again).

RobLC · October 2009

Thanks, NBC, re: vaporstat + code...

Thanks for the picture, looks like a really nice setup you've created for your guages and pressure switches.

I notice that you have 2 BX cables going to the Vaporstat and 1 BX to the Pressuretrol. Why 2 to V'stat?

That is a beautiful radiator.

We have National Grid coming Tues to do the check up/inspection. Our contract will replace anything that's immediately attached to the boiler. I'm sure they won't agree to replacing the P'trol with a V'stat - - price difference is too great. If we want a V'stat, we'll have to pay for it. I'd still like to see what pressure the boiler cuts out on with a replacement P'trol.

What could be wrong with the current one? I took it apart and doesn't seem like much of a mystery.

Thank you, NBC, for the pictures and for taking the time to answer my questions.

RobLC · October 2009

Thank you, Jamie Hall, re: Not particulary...

Yes, good, I agree with you and NBC it's not safe to run boiler without functioning cut out.

It's very possible that this switch has been bad for a while. Usually when the inspection takes place, the tech is done in 15 to 20 min. As long as the boiler fires; doesn't produce unsafe levels of carbon monoxide and the lwco, auto feeder work, they never waited for the kettle to produce steam and then cut out on specified pressure.

Fuel savings and energy savings are always welcome.

Thanks, Jamie Hall, for taking the time to answer my questions.

nicholas bonham-carter · October 2009

we were in your shoes once

it is my pleasure to be helpful, as others were for me, when i was in your situation. not only was i receiving advice; but also encouragement, which was the most important part of my steam experience!--nbc

Steamhead · October 2009

I'll second the Vaporstat

There shouldn't be any Code issues with it.

You might run into Code issues with the gauge, however. The original 0-30# gauge is required since the boiler (but not the system) has a maximum working pressure of 15#. So it has to stay there. However, there's nothing to prevent you from also using the 3# gauge, as long as the original stays in place.

RobLC · October 2009

Thank you, Steamhead, re: I'll second the Vaporstat...

We are looking for a V'stat now, the prices fluctuate wildly for the same model depending on where we buy it.

Yes, we have a 30psi on the front of boiler and a 3psi on the back of the boiler on the pigtail with the P'trol.

I took this thing apart and it sort of reminds me of the distributor points in the pre-electronic ignition days.

Trying to understand why you can't bend the diaphram (if you had to in an emergency) or do something to make the P'trol cut out on a lower pressure if it doesn't want to cut out.

Thank you, for taking time to add to this thread.

RobLC

Runaway Pressuretrol...

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