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palmpilot 12-21-2007 09:09 AM

Baseboard heating overpressure puzzle
 
I'm new to this forum.

I have an old (1982?) HydroTherm gas fired furnace in my baseboard heating system. Although heating worked early this season, I noticed there's no pressure in the system and also I could hear water flow sound on the second floor. Two days ago, I realized the water might be low. (I replaced the discharge valve in summer 2006 and didn't replenish water)

I used the fast fill of the pressure reducing valve (Bell & Gossett) to bring the pressure to 15 psi while the furnace was still hot (risky!). After a while, the pressure went over 30 psi and the safety discharge kicked in. I released some water and the pressure dropped to fast so that the B&G valve recharged water. Finally, I followed B&G's instruction on their site and shut off the city water supply. But the pressure kept going over 20 psi. Yesterday, I took at least 5 gal of water out the system. The pressure can stay around 15 psi for only 4 - 5 hrs. Fortunately the heater is still working!

Sorry about the long message. My questions are:
1. Where's source of the pressure?
2. Do I have bad expansion tank? I touch the tank and the bottom felt hot and top felt less hot.

I greatly appreciate your replies!:( :(

redline 12-21-2007 06:49 PM

How old is the expansion tank?

Did you test the pressure (bladder) in the expansion tank?

palmpilot 12-21-2007 08:14 PM

Thank you, Redline. I guess the expansion tank is 20 year old. How do I test the pressure? There's a small red plastic cap on the top of tank. Can it be unscrewed?

The pressure keeps rising. I drained ~ 4 gal hot water out of the system this afternoon. Surprisingly, the system is still full. I felt the expansion tank and only the lower quauter is hot.

palmpilot 12-22-2007 07:47 AM

expansion tank is fine
 
I used a tire gauge to check the pressure of expansion tank. It's ~ 12 psi.

Overnight, the furnace pressure went up to 30 psi (140 F). I had to drained another 2 gals of water to drop it to 15. Heating still works but I can hear water running in the pipe upstairs now.

Totally confused.

redline 12-22-2007 12:32 PM

Do you get water out of the expansion tank air valve?

When you checked the expansion tank pressure what was the pressure on the boiler?

palmpilot 12-22-2007 01:44 PM

update
 
Redline, no water came out of the valve.

My wife had enough. She had me call for a plumber. The guy replaced the pressure reducing valve and expansion tank. Pressure seems to hold well now. The guy said those two parts are source of odd pressure. Another malfunction can cause pressure trouble is the aquaset is bad and the furnace keeps heating. My aquaset is off 20 F but still works. Any idea how to replace the aquaset? I'm taking no chance and will do the job after the holiday.

I'll keep you posted if there's any new trouble.

redline 12-22-2007 08:43 PM

The tank needed to be replaced.

aquaset or aquastat?


http://www.bellgossett.com/ProductPa...s-Aquastat.asp

bigMikeB 12-22-2007 08:59 PM

Quote:

Originally Posted by palmpilot (Post 82375)
Redline, no water came out of the valve.

My wife had enough. She had me call for a plumber. The guy replaced the pressure reducing valve and expansion tank. Pressure seems to hold well now. The guy said those two parts are source of odd pressure. Another malfunction can cause pressure trouble is the aquaset is bad and the furnace keeps heating. My aquaset is off 20 F but still works. Any idea how to replace the aquaset? I'm taking no chance and will do the job after the holiday.

I'll keep you posted if there's any new trouble.


Do yourself a favor and call the plumber back to change out the aquastat, you could gave blown up the boiler and killed yourself opening a fast fill to a hot boiler that had no water in it. You lucked out this time. That is why even residential boilers now need low water cut offs.

palmpilot 12-25-2007 03:33 PM

bigMikeB, thanks for your remind. I got lucky this time.

After the pressure reducing valve and expansion valve, the furnace has been working fine. The aquastat is off 20 F. But as long as it's set at 160 F, the furnace switch off at 180 F. I leave it alone this winter. Is it complicate to replace aquastat? Dose the well need to replaced at the same time?

Merry Xmas and Happy New Year!

bigMikeB 12-26-2007 12:53 PM

The reason it maybe so far off in temp is a build up of sediment on the well. Typically if you get the same brand aquastat you don't have to change the well but, I would want to take it out and check it out.


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