Hopefully someone here can help guide me in the right direction on fixing my heating system in my home. My house was built around 1959 and has a hydronic heating system with baseboard radiators. We bought the house a little over a year ago and the house had not been inhabited for a couple of years prior to that. Last winter I had a retired HVAC guy I know look at the system and he helped me bleed air out of it (there was quite a bit in it). Since then the pressure has been running high on the system, to the point that the relief valve starts bleeding off. The gauge shows it running close to 30 psi. The guy I had look at it said it was probably the feed valve allowing too much pressure in, but I thought I'd see if there was something else to look for before I put one on. The pressure is high whether the boiler is running or not.
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Hydronic heating pressure issue
- Thread starter dawg69
- Start date
sms1974
Well-known member
Feed or fill valve is a possibility, a bad expansion tank is more likely tho... When you heat water it expands causing the pressure to rise if the expansion tank is bad it can cause excessive pressure and the relief would then open to let off pressure... Sometimes after that happens and the boiler cools down the pressure will go low enough for the automatic fill valve to open and let more water in...
I'd start with the tank, however if your going to drain and open the system you may well end up having to replace the automatic fill valve and possibly the relief valve as well...
The air you bleed out would have acted like an expansion tank, remember you can compress air but not water... That's why your problems started after getting the air out...
I'd start with the tank, however if your going to drain and open the system you may well end up having to replace the automatic fill valve and possibly the relief valve as well...
The air you bleed out would have acted like an expansion tank, remember you can compress air but not water... That's why your problems started after getting the air out...
Thanks. This has the old style tank, not one with a bladder in it. I've drained it a few times, but may just convert it to the newer style anyway so I don't have as much maintenance.
ETA: This seems to happen hot or cold now for some reason if that makes a difference for diagnosis.
ETA: This seems to happen hot or cold now for some reason if that makes a difference for diagnosis.
roscoe2000
Well-known member
Your expansion tank (old style, closed) should be only filled with water around 1/2. The remaining capacity is for the air cushion that with take up any water expansion. Then you fill valve should have a water pressure regulator and that should be set for a minimum of the pressure that is required to keep water up to the highest level in your building. Since your system is dumping while cold, your water pressure regulator valve is over pressurizing your system. 50 psi would put you around 100ft.
Don't even think about it. Just put in new parts. Air separator/eliminator, backflow valve, pressure reducing valve, aquastat, expansion tank, relief valves, gauges, etc. Just do it. Spend $5-600 on your system. It's less than new brakes and tires for your car.
mygarageone
Well-known member
I've backed the adjustment screw on the feed valve/regulator/whatever the correct term is to the point it comes clear out and it still runs high pressure.
Then the diaphragm is stuck , you can actually clean those out . Take the big nut on the bottom off there will be s sceen . You should be able to flush it out there but I have at times had to disassemble the thing completely clean it up and reassemble . But chances are the rubber gaskets will get torn in the process.
If that thing was in active for very long , you ,Might as well replace it . There about $35.00 - $45.00 and worth it as far as I am concerned.
Then the diaphragm is stuck , you can actually clean those out . Take the big nut on the bottom off there will be s sceen . You should be able to flush it out there but I have at times had to disassemble the thing completely clean it up and reassemble . But chances are the rubber gaskets will get torn in the process.
If that thing was in active for very long , you ,Might as well replace it . There about $35.00 - $45.00 and worth it as far as I am concerned.
Thanks. I was wondering if they were serviceable. I may give it a whirl and if it doesn't work out, I'll just replace it.
sms1974
Well-known member
there should be a shut off valve before the auto fill valve, have you tried closing that?
that should stop the relief valve from popping off, then keep an eye on the pressure it should remain stable. if it does then you'll know for sure its the fill valve. also in my experience its about 1 in 25 that you can service and will then work properly, just change it and save yourself the hassles...
that should stop the relief valve from popping off, then keep an eye on the pressure it should remain stable. if it does then you'll know for sure its the fill valve. also in my experience its about 1 in 25 that you can service and will then work properly, just change it and save yourself the hassles...
mygarageone
Well-known member
there should be a shut off valve before the auto fill valve, have you tried closing that?
that should stop the relief valve from popping off, then keep an eye on the pressure it should remain stable. if it does then you'll know for sure its the fill valve. also in my experience its about 1 in 25 that you can service and will then work properly, just change it and save yourself the hassles...
The auto fill valve is only a spring , diaphragm , adjusting screw and a screen .
Unless the rubber seal gets ripped cleaning , it will work . I have done it many times but only when I had no alternative .
sms1974
Well-known member
The auto fill valve is only a spring , diaphragm , adjusting screw and a screen .
Unless the rubber seal gets ripped cleaning , it will work . I have done it many times but only when I had no alternative .
25 years in HVAC and I can't think of more than a handfull of times I've been able to get one to work correctly and reliably after they stuck open or closed... Of course on my side of this time is money. do I spend an hour to strip clean and reassemble then hope it works, or and hour replacing it with a new part that's warrantied and I know will work...
mygarageone
Well-known member
25 years in HVAC and I can't think of more than a handfull of times I've been able to get one to work correctly and reliably after they stuck open or closed... Of course on my side of this time is money. do I spend an hour to strip clean and reassemble then hope it works, or and hour replacing it with a new part that's warrantied and I know will work...
I have said changing it is preferable , but when you have no choice it can be cleaned.
They are made to be cleaned and repaired other wise there would be no way to disassemble them.
There was a time , before your current time that stuff like this got cleaned or repaired , not always replaced.
But that was before we became a throw away society , I recall many times repairing toasters , furnace , boiler parts etc .with my dad . But that was in the 50's and 60's .
Yes I'm old enough to have done that but not so old I have forgotten it.
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sms1974
Well-known member
All good... The real problem is nothing is made worth a **** these days...
tcianci
Well-known member
One thing that no one mentioned...does the system have a tankless or indirect water heater? You need to remember that the potable side of the water heater is at street pressure and a pinhole between the potable side and the boiler side will constantly overpressure the system. Closing off the valve before the fill valve essentially takes the fill valve out of the equation, so now all you have is the boiler and the expansion tank and heat. It's a good first stab at troubleshooting the system.
mygarageone
Well-known member
All good... The real problem is nothing is made worth a **** these days...
Yes quality does not exist anymore.
Yes quality does not exist anymore.
The rare times that it does it's a special order/non stock item.
fill valve /regulator is defective. I also bet that 30 PSI is the high pressure blow off setting.
Thanks for the input so far guys. I thought I'd give an update as to where I stand with this issue. Yesterday I took the auto fill valve apart gently and got the diaphragm to move as much as it appears like it should. I did go to my local hardware store to see about a new one and they could order one at $90 or they had a complete assembly with the relief valve and fill valve for over $200. I thought I would hold off until I knew 100% that it was the issue.
It was mentioned about closing the valve before the auto fill valve and I've done that and the high pressure still exists. I didn't get a chance to check pressures today, but I didn't see quite as much water in my catch container under the relief valve as what had been there before. I did see it dripping though, so it must have been relieving pressure at some point.
It was mentioned about closing the valve before the auto fill valve and I've done that and the high pressure still exists. I didn't get a chance to check pressures today, but I didn't see quite as much water in my catch container under the relief valve as what had been there before. I did see it dripping though, so it must have been relieving pressure at some point.
sms1974
Well-known member
Drain your expansion tank or replace it with a new diaphragm style tank...
I don't see how you are going to get pressure into the system other then the feed line -- the real old auto feeders work forever the newer ones (15 years) -- are junk.
Dump the pressure -- and use the valve on the autofeed to fill the system. then shut the valve. In my systems I keep them about 12psi cold ... naturally move up hot.
The old tanks work -- the new tanks with a spirovent are much better
Dump the pressure -- and use the valve on the autofeed to fill the system. then shut the valve. In my systems I keep them about 12psi cold ... naturally move up hot.
The old tanks work -- the new tanks with a spirovent are much better
k p
Well-known member
I have a hydronic heating system too, I had to drain my expansion tank (non-bladder style) for this exact problem last year. My 30psi pressure relief valve was dripping water each time the boiler fired up.
On my expansion tank there's three valves... one valve which seperates the tank from the rest of the system, one valve to drain the tank and the third valve is at the top of the tank to allow air in while it's draining.
My expansion tank is an old steel unit and I actually found that the water wasn't fully draining because rust was clogging the drain valve. I used a plastic mallet to hit the valve a few times and you wouldn't believe the crud that came out.
I suggest taking one more stab at draining the expansion tank.
1. Close the valve that seperates the tank from the rest of the system (so it doesn't continue filling as you empty it).
2. Open the tanks drain valve, the expansion tank will have 30 psi in it as well and will push water out on it's own. Once the water stops draining go to #3.
3. Open any valve you can see at the top of the tank to allow air in while the remainder of the water drains.
4. Close the top valve, close the drain valve and re-open the seperation valve. Your tank should now be full of air and will re-stabliize your system pressure (hopefully).
Best of luck!
On my expansion tank there's three valves... one valve which seperates the tank from the rest of the system, one valve to drain the tank and the third valve is at the top of the tank to allow air in while it's draining.
My expansion tank is an old steel unit and I actually found that the water wasn't fully draining because rust was clogging the drain valve. I used a plastic mallet to hit the valve a few times and you wouldn't believe the crud that came out.
I suggest taking one more stab at draining the expansion tank.
1. Close the valve that seperates the tank from the rest of the system (so it doesn't continue filling as you empty it).
2. Open the tanks drain valve, the expansion tank will have 30 psi in it as well and will push water out on it's own. Once the water stops draining go to #3.
3. Open any valve you can see at the top of the tank to allow air in while the remainder of the water drains.
4. Close the top valve, close the drain valve and re-open the seperation valve. Your tank should now be full of air and will re-stabliize your system pressure (hopefully).
Best of luck!
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BadgerBoilerMN
Well-known member
You can lead a horse, but you can't teach him hydronics.
Replace the pressure relief valve, every 5 years.
Install a proper air eliminator upstream from the pump #30 diaphragm expansion tank and attach to the bottom of the new expansion tank. We use PowerVent, Spirovents and Taco Vortex vents.
Fill the system however you can and leave it at 12 psi. All water off.
Replace the pressure relief valve, every 5 years.
Install a proper air eliminator upstream from the pump #30 diaphragm expansion tank and attach to the bottom of the new expansion tank. We use PowerVent, Spirovents and Taco Vortex vents.
Fill the system however you can and leave it at 12 psi. All water off.
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