Defective Pressuretrol?

Jon_12

I have a low-pressure residential boiler, approx 15 years old, that recently does not develop pressure. I hear a switch trip it off after it fires for about 5 minutes (and just starts steaming); the boiler then goes through rapid light-off/trip cycles. Water level is fine, and LWCO was recently replaced. The Honeywell pressuretrol (PA404A) is set at 0.5 psig, differential at 1 psig. Any suggestions on the likely cause?

Unknown

Is it a probe type LWCO ?

Did the problem start right when it was replaced ? Sounds like the symptoms of a hot water LWCO on a steam system .

Gary_17

pigtails

You should make sure the pigtail isn't partially plugged.

will smith_4

break out a meter

-and see which switch is opening the circuit. You don't happen to have an automatic damper in the flue, do you?

Jon_12

Good idea, but ..

It was a direct replacement of the old M&M 67. I thought the old one might have been the problem (it was 15 years old too), but same symptoms before and after replacement.

Jon_12

There is a damper on the flue with a contact switch as proof open. The damper remains in the open position when the boiler trips off.

Jon_12

I primed the pigtail with the blowdown valve open to make sure it drains through (it did). I then closed the blowdown valve and add a bit more water before reconnecting the Pressuretrol at the top.

will smith_4

Another-

Possibility is that the flue damper switch is doing the old "cheapest part fails first" routine. Can't tell you how many of these I've seen cause service calls; they have to prove open before they allow firing, and the prove switch likes to, well, not prove.

Gary_17

differential

Try raising the differential to 2 or 3 to see if that makes a difference.

Jon_12

good idea

I'll check it, but the boiler consistently fires correctly when the thermostat initially call for heat (damper opens, switch makes, and boiler lights off). It trips after 5-10 minutes of firing, then goes through multiple resets/trips cycles. The pressure gauge on the boiler never moves, even if I increase the DP setting on the pressuretrol. Hence my suspicion of the pressuretrol.

Jon_12

nope ... How to test pressuretrol?

I tried raising the DP settings, but no change. The boiler never fires long enough to build pressure. Can you suggest a way to test the pressuretrol?

will smith_4

Sure Jon-

I use some of the goodies I keep in my pneumatic test/calibration kit. A hand pressure pump attatched to a tee, with a nipple you attach the pressuretrol to, and a gauge to tell you the pressure you're sending it. Since the pressuretrol you're using doesn't have a mercury switch, being level isn't important; just slowly pump up the pressure with an ohm-meter placed between the normally open contacts of the 'trol, and see at which pressure the contacts break, then slowly bleed off the pressure and see where it makes. If you can't get it cut-in/out where you want, send it packing!

Jon_12

clear and simple ...

Thanks Will - hopefully this will help me find the root cause. At least I'll know if the pressuretrol is working correctly!

Al Gregory

Is it an electronic LWC is it a Safe Gaurd? They stop the boiler every few minutes to perform a self check