View Full Version : Oil Fired Furnace High Pressure Problem
05-02-2007, 12:07 PM
We have exhausted most of the obvious to try and correct this high pressure problem however it continues. We have an older weil-mclain oil fired furnace which would cause the Pressure Release Valve to pop and release water. After replacing the valve twice the problem continued. We decided to replace the old expansion tank with a new diaphragm style tank, replace the pressure release valve as well as the main water pressure regulator. After this the running average pressure is even higher than before 23-25psi vs 17-19psi. The pressure spikes when the furnace is called to come on (as would be expected). Air also seems to keep getting into the radiators which we bleed. They seem ok for a few days/week and the air returns. I assume this might be excess steam getting back into the system. The furnace temperature is set to 140-160F which I donít think to be too high. Our plumber and us are at a lose for what the potential problem might be. Is there something we are overlooking? Is the temperature set to high? Any help would be greatly appreciated.
05-02-2007, 04:11 PM
If you don't get the air out of the system, when it gets heated, it will expand much more than the expansion tank can handle, and you might have damaged the new one you put in. They are not designed to have the bladder fully extended. Air expands and contracts much more than water does, so having a little air in the system can cause pressures to vary much more than just having water in there.
Do you have an automatic air extraction system on the boiler lines? If not, I think you should have one added. But, you also have a leak somewhere. It may go away when you can limit the pressure to the normal range, which is often between one atmosphere (around 15 pounds) and 20 or so. The T&P valves often pop at not much over that pressure.
05-03-2007, 12:12 PM
I'm actually not sure if I have an automatic air extraction system. I would guess not since I don't know what it is. I'll have to check the tank to see if the bladder failed and see if the tank is filled with water. I last I check if didn't.
Where would this automatic air extraction system be placed. After the diaphragm expansion tank, before it, or somewhere else. We have a little (tiny) canister on top of the boiler like which appears to be a air release valve of sorts. I was under the impression that that was a air release valve. I'll have to check better for leaks, none obvious so far.
05-03-2007, 02:09 PM
That little can should let some air out... http://taco-hvac.com/en/products/Air+Vents/products.html?current_category=87 they can get gummed up or rusted inside and stop working. Something like a Sprirovent http://www.spirotherm.com/air/ works well (better than, but not in place of the one you have). Other companies may similar things. The leak may not let water out, but could let air in when things cool off, contract, and create a slight vacuum.
joe in queens
05-04-2007, 02:23 PM
Is your boiler used to produce DWH?
If so try shutting off the water supply to the coil, initiate a call for heat and see if the pressure still rises beyond what's normal. If the pressure no longer gets out of control, chances are the coil is leaking.
Also try shutting the water off to the boiler altogether, initiate a call for heat and see if the pressure rises. If the pressure no longer gets out of control, your auto fill valve is bad (if in doubt, just replace it) or your water pressure exceeds the capacity of the auto fill valve. A PRV might be needed at the boiler, or a higher input pressure PRV - or both.
I also agree with others here on a SpiroVent... certainly can't hurt.
05-07-2007, 09:57 AM
I was able to watch the boiler a little closer this weekend in the middle of my basement bathroom project. Basically this is what I observed.
First off, I noticed that I have the boiler set to go on and off at 140/160 degrees. I noticed however, that the boiler fires at 160 not 140 and it shoots over to 190 with the continued run up (I know that run is standard). The temperature would drop to 160F it would fire the starting pressure was between 8 and 10 PSI and would rise with the temp. to 180-190F and 16PSI.
The Pressure Release valve went off early in the morning after I noticed the baseboard heat come on. I also noticed that there seemed to be air in the radiators. My novice assumption is that it might be related to the radiator side of things and not the DHW (domestic hot water). As well as air getting into the radiators. I didn't get a change to isolate the lines to check for the rise in PSI, etc. Will do that next.
The radiators came on this morning (Monday) due to cool morning (Twice) and no issues were noted. I also noticed that I did not hear any air in the radiators this morning. Pressure held at about 18-20 with the boiler fired.
I was able to take some pictures of the system the pressure regulator (12-15psi), expansion tank and the boiler itself. I also have an unknown part picture which I have no clue what it is. It's connected from the boiler radiator pipe which leads to the upstairs baseboards.
http://i207.photobucket.com/albums/bb110/therightsolution1/Unknownpart.jpg http://i207.photobucket.com/albums/bb110/therightsolution1/MainPressureReducingValve.jpg http://i207.photobucket.com/albums/bb110/therightsolution1/DiaphragmExpansionTank.jpg http://i207.photobucket.com/albums/bb110/therightsolution1/Boiler.jpg
If the air continues could I but in an automatic air release valve in one of the baseboards upstairs? The system already has little air release bleeder canisters. Whenever I try to release these only water comes out.
John in herndon
05-27-2007, 10:31 AM
The green mystery valve is a thermo-siphon flow preventer. In the normal position it prevents thermo-siphoning. This is necessary to prevent the baseboards from heating up in the summer when the boiler is being used for DHW.
In the event of circulating pump failure the valve can be manually opened (small lever near the top) to allow the baseboard units to receive some hot water and heat up, although not at full capacity as it would with the pump.
In some gas boilers with millivolt controls it would also allow you to keep your house warm in the event of a power failure. (A great feature and one which justifies the retention of an old standing pilot unit)