Odd pressure increase in recent days....

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Posted by Jeremy Anderson on December 27, 2001 at 06:10:18:


I'd like to thank you in advance for taking the time to read my post and for providing any assistance as possible.

I just recently bought a house last spring that is heated by a gas-steam boiler. As far as I can determine the boiler is a Weil-Mclain that was installed somewhere around 1981. It heats a two story house via 9 single inlet radiators.

Before starting it this season I had a pre-season cleaning and inspection. The guy didn't do much but clean the burner rods and verify that the burner engaged properly and visually inspected the safety cutouts. (He wasn't too familiar with servicing steam boilers). He also recommended I spend $700 to convert the manual H20 feed to an automatic assembly. I also asked what the normal operating pressure is for these boilers, and he responded 'not much more than 1-2 psi'.

Starting Christmas Eve the boiler began acting up. I noted the pressure was up near 3psi and fiddling with the thermostat had no effect. I was able to get it to engage twice when I gave a good tap to the pressure reader. My uncle took a look at it and noted that the pressure cut-in worked properly, but was set rather close to the current pressure in the system. He adjusted it and the problem went away from the 25th to the 26th.

At this point I noted that the burner remained engaged past the temperature point set on the thermostat. The temp is set to 64 and the burner continued to fire until the temperature reached 67, then at that point the temp continued to rise due to the radiant heat stored in the radiators.

So last night I fiddled with our thermostat. We have an older dial thermostat that has the needle set on top and the current temp on the bottom needle. When the initial problems began I had noticed a small metal needle on the bottom side of the thermostat when the outer cover was removed and had fiddled with it. Last night I noticed it had the text "longer .12 .25" and then a series of notches. (The text was at 3o'clock on the thermostat and the notches ended around 6o'clock on the thermostat)

I scrapped the paint off of it and moved the needle closer to the beginning of the scale (3:00) from the opposite end where it was currently set (6:00). (I assumed this was a delay switch, causing the burner to continue to fire after the set temp is reached)

Well, this morning, the 27th, I awoke to discover the house temp at 58, with the thermostat set to 64. I immediately thought the pressure cut out was exceeded and went to look at it. Sure enough the boiler pressure was now at 4psi, close to the cut-in. But adjusting the cut-in above 5psi had no effect on the heater. If I turned the temp on the thermostat up to 70 I could get the burner to fire only if the 'longer' setting on it was set to 6:00. I also noted the ‘longer’ needle was not in contact with the notched scale unless it was in the 6:00 position. Does the needle need to be in contact to complete a circuit?

I didn't have much more time to fiddle with it, because I was already late for work. I am left with the notion that I may need to pick up a new thermostat on the way home tonight. I am beginning to think that our current thermostat may be contributing to part of the boilers odd operation as of recent.

If you've taken the time to read all of the above, I thank you very much. If you have any ideas as to how I should proceed they would be greatly appreciated. Also if you could answer these questions it would help me as well:

* Is the recent increase in pressure of the system normal? Is it a sign that something more is occurring? It used to remain around 1-2 psi, but now is slightly above 4psi.

* What is the 'longer' needle on the underside of the thermostat? What does it control? Does it need to be in contact with the scale to complete a circuit?

Thanks again for any help you can provide.

Happy Holiday's!!

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