Single-Pipe Steam in Queens: Pressuretrol Won’t Fire Below 2.5 PSI — Upgrade to Vaporstat or Leave A

cjdesimone4

Hi everyone,

I live in Queens, NY, in a home with a single-pipe steam heating system. A local plumbing company installed a new gas steam boiler in basement with two floors above it for us when we converted over from oil.

The installer says it is OK to leave the Pressuretrol set where it is, but I read online that residential steam systems should run at a much lower pressure (around 0.5 PSI cut-in).

Currently, my Honeywell PA404A Pressuretrol is set with a cut-in around 2.5 PSI and a differential around 1.

Here is what I'm seeing:

1. Whenever I attempt to lower the cut-in dial on the front scale below 2.5 PSI, the boiler will not fire at all.

2. When I inspect the internal microswitch and press the button next to the differential, it does not click when set low. It only operates on the lever once the dial is back up to ~2.5 PSI.

My questions for the group:

 Should I leave it alone as the plumber suggested, or is it better to get the operating pressure lower?

 Is my PA404A just too stiff/insensitive to operate at 0.5 PSI, or is this typical for these bellows boxes?

 Is it worth getting a Honeywell Vaporstat (like an L408J or an older mercury L408A/B off eBay) so it can operate at 0.5 PSI?

I'd appreciate any advice from the steam community on how to handle this setup.

pecmsg

How are you measuring the pressure, with the gauge on the boiler? That is not accurate much below 10 or 15PSI.

EBEBRATT-Ed

The Pa404a the scales are inaccurate and they can be difficult to dial in.. Before you go to the expense of a vapor stat which is $$$$ I suggest you buy a low pressure 0-5 psi pressure gauge. You can stick a tee on someplace to add the gauge next to the pressure control etc. Its better if the gauge is protected by a pigtail. Use all brass fittings.

Make sure the pigtail and the pressure control connections are clear while you at it.

Once you can see the accurate pressure you should be able to adjust the control to cut in just above 0 and cut out at 1.5-2psi.

Did they size the new boiler to your existing radiation (measure the rads)?

Pictures of the install may help.

cjdesimone4

https://forum.heatinghelp.com/discussion/comment/1907497#Comment_1907497

Good point about the gauge! I'm currently using the standard 0–30 PSI boiler gauge, so I know it isn't precise down in the ounces.

My main question isn't so much about reading exact numbers on that gauge, but whether the boiler should be running at a lower operating pressure overall, and whether upgrading to a Vaporstat is the right move for my single-pipe setup.

Since the installer left the Pressuretrol cut-in around 2.5 PSI (and the burner won't fire if I set the dial lower because the microswitch doesn't trip), I'm trying to figure out:

1. Is 2.5 PSI cut-in simply too high for a residential single-pipe steam system in a house?

2. If I mount a 0–30 oz low-pressure main gauge (a 0–3 or 0–5 PSI gauge) and a Honeywell Vaporstat, is it worth the upgrade to get the system operating down at 0.5 PSI cut-in / 1.5 PSI cut-out?

cjdesimone4

https://forum.heatinghelp.com/discussion/comment/1907499#Comment_1907499

Thanks for the feedback!

One thing I'm trying to figure out for sure is: if the boiler physically will not fire at all when I set the cut-in dial below 2.5 PSI, does that mean my current PA404A is just incapable of handling lower pressure, or is there something else blocking it?

Given that limitation, is 2.5 PSI considered too high of a pressure for a single-pipe residential steam setup, and is it worth switching over to a Vaporstat specifically so I can get it running down near 0.5 PSI?

cjdesimone4

https://forum.heatinghelp.com/discussion/comment/1907503#Comment_1907503

cjdesimone4

https://forum.heatinghelp.com/discussion/comment/1907503#Comment_1907503

Jamie Hall

The PA404A is an additive pressure control device. On the outside, there is a scale for cutin, which can be set as low as 1 psig — though I would suggest slightly higher is better. On the inside there is a differential wheel which should be set to 1. That should give you a cutout pressure of a bit above 2 psig — which is the most you want for residential steam — and a cutin of a bot above 1 psig.

If the control is operating properly, it is quite satisfactory for most residential steam systems (not for vapour — ow pressure — two pipe systems, but that's a different matter).

As suggested, get a low range pressure gauge and add it to the pigtail with the pressuretrol and see what is really happening. The 0 to 30 gauge, which is required by code, is none to accurate at low pressures.

cjdesimone4

https://forum.heatinghelp.com/discussion/comment/1907507#Comment_1907507

Thanks for breaking down the additive scale on the PA404A!

That makes total sense regarding how the cut-in dial and internal differential wheel work together (Cut-In + Differential = Cut-Out).

The issue I'm running into is that on my specific unit, whenever I move the front main scale dial down below 2.5 PSI (trying to target that 1.0 PSI cut-in), the microswitch opens up and the boiler physically will not fire at all. The internal lever/switch only responds and allows the burner to ignite when the main scale dial is set up at roughly 2.5 PSI or higher.

I'm definitely going to install a low-range 0–5 PSI gauge on a brass tee off the pigtail to verify the exact pressure readings as suggested.

In the meantime, if the main scale won't let the burner fire when set near 1.0 PSI, does that sound like an internal calibration/stiffness fault inside this PA404A, or is upgrading to a Vaporstat the standard fix for getting down to that 1.0 cut-in / 2.0 cutout range?

Jamie Hall

Get the pressure gauge and check — but it's not unheard of for a PA404A to be out of calibration — but not, usually, that far! Vaporstats are not cheap — and in my opinion they are overkill for one pipe and most two pipe steam systems.

After you get the low pressure gauge, if you find the PA404A is lying to you you can try to recalibrate it — there is an adjustment screw — or simply set it so that the gauge reads a 2.0 psig cutout/1.0 psig cutin and write a iittle note to yourself…

EBEBRATT-Ed

You should be cutting IN as low as you can. Just above 0 or as low as the control will operate. The cut out should never exceed 2 psi. 1.5 is usually good.

But that depends on the boiler sizing in comparison to the radiation. Too low of a differential will short cycle with an oversized boiler. Sometimes you have to compromise.

My first post I forgot to mention the differential wheel inside the control.

109A_5

Your Pressuretrol is probably not calibrated correctly, simply run the settings at the lowest setting that provides reliable operation. Once you get a suitable gauge you can try to calibrate it if you want to tinker with it.

The Pressuretrol is a limit device not a pressure demand device. If the boiler is sized correctly or undersized the Pressuretrol is useless other than a safety device. It should never trip. Since the boiler can't produce more steam than the radiators can dissipate (or condense).

As an example my house heats just fine at less than 0.072 psig. So the Pressuretrol is just a safety device and a Vaporstat would be a total waste of money.

The way it sounds you don't know if your Pressuretrol ever trips. Your system may heat your house with under 2 Inches of Water column like mine does.

You need to get gauge(s) 1-5 psi, 1-3 psi, 0–30 oz, or even Inches of Water column or build a manometer on the system to realize exactly what is gong on. Then make informed decisions.