Steam boiler pressure issue

ajreed312

Hello everyone. I am an HVAC service tech with 12yrs experience but only 4yrs of boiler experience. I am new to this website and I’m having an issue with a residential 2 pipe steam boiler building too much pressure within 10 minutes of run time. The original call was to just do a preventive maintenance on the boiler this morning and it was the first time that the boiler had fired up the season. At one point the boiler was operating over 10 psi according to the gauge. I did find that the siphon tube is blocked and the pressure gauge was reading 2 psi higher than what the actual pressure was. I cleared the siphon tube and verified that the pressuretrol was not plugged. After putting everything back together the boiler was still running too high of pressure. At that point I replaced the pressuretrol (Honeywell PA404A) and pressure gauge because I thought if the system is running over 2 psi then the pressuretrol should be shutting the burners off and it was not. After replacing the pressuretrol, the system is still running at too high of pressure. I shut the boiler off once it reached 7 psi on the new pressure gauge. I did set the cut in psi to .05-.06 and the cut out to 1 psi. That is what I typically set them to. The pressuretrol is tee’d off from the top sight glass valve. I removed the sight glass, top valve and verified that it was not blocked. It was clear. I am running out of ideas as to why the boiler is still firing with a operating pressure above what the cut out pressure is set to. The boiler can’t run long enough for the radiators to start heating so I cannot check the temperature differential across the traps. Any help would be much appreciated.

JUGHNE

If you take one wire off of the control terminals does the burner shut down?

Fred

Did you calibrate the Pressuretrol before you put is on? They are typically way out of calibration, maybe even a bad unit. If you are sure the pigtail isn't clogged, that Pressuretrol should shut the boiler down at about 2 PSI. Are there any gate or King valves on any of the mains that may have been closed? Are there any failed crossover traps that may be failed open, letting steam into the returns?

ajreed312

I did remove one of the wires to the pressuretrol and it did shut the burners off. I had 24v to ground on both terminals and 0v across while the boiler was operating over the designed pressure. I did not calibrate the pressuretrol before I installed it. All I did was set the cut in/out settings. There are no gate valves on the mains and the main vents are open when the boiler is running. The main vents do have a 6” risers from the mains. I have not checked the thermostatic traps yet.

JUGHNE

Did you try to operate the pressure lift plate inside the control with a screwdriver? The switch could be stuck.
With an ohm meter connected,you can blow into the switch to verify operation.
How many screws are on the switch?

Picture of the control, pigtail and gauge would be nice.

ajreed312

I did move the plate with a screwdriver and it did shut the burners down. I will post a picture once I’m on site again. Thanks.

JUGHNE

Did you prime the loop with water?
There is one situation I have never heard of, but only imagined:
Loose fittings that does not let the pressure get to the control.
Or a cracked fitting....seems like you would notice the steam though.
That sounds like a long shot, doesn't it?

ajreed312

I did prime the siphon tube before I installed the new pressuretrol. My service manager is going to try and get a boiler guru from the local distributor to meet us on site and see if he can figure out the issue. If it is something that I didn’t simply overlooked then I’ll let you guys know what we find. Thanks for your advice.

JUGHNE

Sometimes adjusting those controls right down to the bottom or beyond causes the internal linkage to come apart and may not shut the switch off.

You would let us know either way....right.

ajreed312

I have learned the hard way about adjusting the switches too far and having problems when the boiler would shut off it would not come back on when it called for heat again because I adjusted the screw too far. I have been setting the cut in pressure to 0.5-0.6psi (or slightly above 0.5)

Fred

If that Pressuretrol is mounted on top of the sight glass, did you also check the Tee to make sure it is not clogged?

Jamie Hall

If the burner stopped when you lifted one wire, at least the general circuit is working as it should. And if it stopped when you lifted the plate, the microswitch is working as it should. Both of which are vaguely encouraging. What is not happening is that steam pressure doesn't raise the plate -- either something is stuck or the pressuretrol doesn't see the pressure. Some troubleshooting -- or try a different pressuretrol.

Now, however, you have a different problem as well -- the boiler shouldn't raise the pressure anywhere near that high in 10 minutes, unless it's working against a closed valve -- which you say you don't have -- or unless it is more than usually ridiculously oversized. Locate all the main vents and make sure that they are operating properly. There will be vents on the dry return(s); there may or may not be vents on the mains, but if there aren't, there should be crossover traps at the ends of the mains.

A note: if the pressure really was that high, which I don't doubt, it is likely that at least some -- if not all -- of the traps are toast, and the vents may be too.

ajreed312

I know one of the main vents is opening when the boiler is producing steam. I’m not sure if the second main vent is opening, because it is hard to get to that vent. I don’t know when I will return to that call, since it is mild where I live and the customer is out of town currently. Whenever I go back, I plan on installing a temporary gauge where the pressuretrol is located to see what the actual pressure the switch is seeing. This seems like a dumb question, but is there anyway that the wet returned might be clogged?

nicholas bonham-carter

10 psi will push the water level in the wet returns high up into the dry returns, obstructing the main vents.
Putting an accurate gauge, (and possibly a vaporstat) on will verify the pressure.—NBC