Delayed closing of gas valve

Wayne Heid

I recently installed a Smith GB-250-9 steam boiler that works fine until the call for heat is removed. At that point the damper closes but the gas valve remains open for another 30 seconds or so. When it does finally close, it closes slowly. Sometimes trickling a small amount of gas for another minute or so that slowly burns at the closest orifice on the manifold. I've verified that no voltage is present at the gas valve. I've even removed the power terminals and the valve remains open.



This boiler has a White-Rodgers 36C53-418 gas valve. Inlet pressure is measured at 6.75” WC (static) and drops to 5.25” WC under flow. Manifold pressure is 3.5”. It also has a Honeywell Pressuretrol as a secondary hi limit connected to the ECO terminals on the gas valve. When one of the ECO terminal connections is removed from the gas valve, it closes immediately.



So far I've changed the gas valve and the problem persists. WR factory support says the pressures are within spec and suspects the Pressuretrol connected to the ECO is somehow causing the problem. I haven't had an opportunity to check that theory but I'm doubtful it's related.



Anyone else have a similar experience or care to weigh in? I'm running out of ideas.



Wayne

JStar

Gas valve

Can you connet the Pressuretrol in series with the thermostat instead of the ECO to see what happens?

Steamhead

Check to be sure

one of the wires going from the ECO terminals to the pressuretrol isn't grounded somewhere. Try an entirely different piece of wire and see if it works as it should. 

Wayne Heid

Sure, I can do that.

What would you expect for results when connected this way? Are you thinking it would prove or disprove a Pressuretrol problem?

Wayne Heid

The wiring is all exposed

so trying new ECO wires to the Pressuretrol should be no problem. I was also going to eliminate the Pressuretrol altogether (temporarily) by installing a jumper on the ECO terminals. I can't see where that would help with a delayed closing but at least it would eliminate the ECO or Pressuretrol as a contributing factor.

icesailor

Strays

Or maybe a little stray voltage in the neutral.

Odd polarity?

Tim McElwain

I looked up the valve

and it is a 24 volt standing pilot 3/4 x 3/4 gas valve slow opening. It should have a three terminal wiring connection with TH - TH/TR- TR the valve coil is between the outer TH and outer TR. Were is the ECO wired on the valve? Some of these valves were not redundant (dual seated) 1979 code required all gas valves from then forward be dual seated, so they used a back up pressuretrol set at a higher pressure to actually shut of the millivolts and used a junction block type thermocouple with the second pressuretrol tied into the junction block. Is this what you have?

Wayne Heid

Yes, that's exactly what I have.

The secondary or backup pressuretrol is wired to what you refer to as the junction block in the thermocouple circuit. The 24V connections are connected to the TH & TR terminals. The TH/TR terminal is not used. The boiler is for process heating in a small batch distillery and the call for heat is initiated by a manual switch instead of a thermostat.

Tim McElwain

The pressuretrol

attached to the junction block on the thermocouple has nothing to do with voltage to the gas valve so it is not your problem.



With the new gas valve if power (24 volts) is removed from the gas valve (disconnecting TH and TR) does the valve close completely? If it does then the valve is okay.



Did you replace the old gas valve with an exact replacement?



If the problem is that when the manual switch from the distillery is shut off the valve will not close then you have a voltage issue due to a faulty manuals switch or a voltage feed from some other source.

Wayne Heid

When the 24V terminals are removed

from the gas valve it does not close. It will close gradually after about 30 seconds and even then it sometimes leaks by just a little for another minute or so with a tiny flame at the orifice closest to the gas valve.



Yes, I replaced the gas valve with the same model.



Yes, the valve stays open when the switch is shut off but as I mentioned above it will stay open for 30 seconds or so whether or not the 24V terminals are connected at the gas valve. I've also measured the voltage at the TH & TR terminals and it drops to 0 when the switch is shut off.

j a_2

Standing pilot

This does not pertain to existing problem however I am wondering why you had a standing pilot boiler installed..In my area they are not allowed to be installed anymore and has been that way for a while....Thanks

Tim McElwain

I just reread

your post and you stated this boiler was recently installed by you so it is in warranty. By the sound of things you have another defective gas valve with that I would also involve the supply house who sold it to you so H.B. Smith can get involved.

j a_2

agreed

However strange, it does appear a second bad valve...I highly suggest calling a trained and qualified tech,   Not to long ago I had a miss wired boiler and  it took some of my time to correct, I billed the manufacture, thru my supply house,I was paid in full, for my time...Just make sure you are correct...BTW you did check the gas line sediment trap, and you did not use ptfe tape near the valve,correct, I do not use it but some do...I hope you keep us informed of the results, this is a interesting post...Imagine if slow closing became a no closing, results could be tragic....

Wayne Heid

I've involved the supply house.

They've involved Smith and Smith supplied the replacement valve. I've also called WR support as well. Everyone seems to be stumped.



I see why you would think the second valve is also bad. I'm considering a switch to a Honeywell valve.

Wayne Heid

The boiler was purchased and supplied

by the owner before I was involved. I would have suggested spark ignition but standing pilot is still allowed here.

Wayne Heid

Yes, I checked the sediment trap.

And no teflon tape used here. I'll keep you informed of progress. Haven't been able to access the site to try some of these suggestions as the owner is out of town for long stretches at a time. So if I don't post progress it's not because I don't value all of your wisdom. I'm just limited to access to the equipment. Thanks everyone!