Burnham goes overpressure in the AM

[JD12345]

Hi All - I hope you can help me - chasing ghosts, and have lurked on here for awhile.

I have a Burnham V8 Series that goes over pressure (PRV drips) in the AM, when all the thermostats turn up.

Max pressure it hits is 40-45 PSI (right above red line on gauge). When not running, it's in 10-20 PSI. And I have never seen it run near the redline except in the AM. I'm in the basement a fair amount so I think I would notice.

The expansion tank was replaced 3-4 years ago - was having the same issue. At that time, the ultimate fix was the pressure reducing valve. That was also probably the last time the system was drained / refilled.

The aquastat is set at 120 - 180 with a diff of ~18. Two story, ~2k square foot house. Last year I had the issue 1-2 times when it was very cold but it stopped and I didn't give it another thought. Right now - it's not that cold by NY standards.

Any thoughts on what I should try next?

 

[Reach4]

The problem may be that your thermal expansion tank needs the air precharge adjusted. I am not sure what the recommended period is for checking that, but I would guess they prescribe annually. It may be the tank needs replacing. It may be the tank is undersized. I don't know boilers, and I did not look at your numbers.

 

[Sponsor]

 

[Fitter30]

Cast iron boilers minimum operating temp return water is 140. With boiler temp 100° or less and all pumps off with a low pressure tire gauge check the air pressure in the ex tank. Should be at boiler pressure 10-12 lbs if water comes out ex rank needs ro be replaced. Use a bicycle pump to add air if needed. Unless you have a optional boiler pressure boiler 40 or 50 lb it usually a 30 lb. Look at name plate and relief valve tag they should be the same.

 

[GrumpyPlumber]

I'm guessing your T-stats are timed to kick up heat in the morning.

A dripping "prv" - I'll guess you're referring to the pressure relief valve or backflow preventer that's in line with the water autofill.

A boiler's relief is set to open at 30psi, static (cold) pressure should be 12-15 psi - You need to verify this pressure first, there are two potential causes for your problem, 1 - the expansion tank, 2 - the autofill.

Tick the expansion tank with your finger and listen to tone changes as you move up/down it's height, you should hear a metallic ring as you approach the inlet end, if not, it's possibly water logged. If there's air in the tank, then you may have an undersized tank if it's not the autofill causing trouble.

If the autofill's the problem, that'll be evident with static pressure, in this case if your boiler reads above 15 psi when cold you can try reducing pressure by closing the manual shutoff water supply before the autofill, draining water until pressure reads 15 psi, spinning off the fast feed lever on the autofill, loosening the lock nut and then turning counterclockwise a tiny bit - reopen the manual valve, if it still fills too high, repeat this process - don't forget to retighten the lock nut when done.

Be careful not too drain too much, if the problem turns out to be a defective autofill, you'll need enough pressure for the boiler to function until it can be replaced.

 

[JD12345]

Thanks very much you all...really helpful.

A couple of follow-ups:
-you think that upping the aquastat min will keep it from over pressuring? Or is that just an aside?
-Is there any reason to not just replace the expansion tank? They're pretty inexpensive.
-Is there any reason to drain the system to clean it out? I've seen mixed messaging on whether that's helpful (clears any blockages) or detrimental (creates a new oxygenated input to the system, can lead to rust)

-Also - Grumpy - thanks for the response.
-Yes - tstats set to come up in the AM. I've thought about reducing the delta between night and morning, but I assume the boiler is intended to handle that kind of jump.
-I don't think it's the autofill - that's what I replaced just a few years ago, and static pressure seems to be right at 15
-For some reason this boiler's pressure max is in the 40s and it's running up there. Is this just an idiosyncrasy of my system?

 

[Fitter30]

At 40 psi relief should be wide open they only drip around setting. Check the ex tank pressure just takes a few minutes. The higher the temp the more the water expands.

 

[Reach4]

When the system is cold, the expansion tank should be empty of water. You may be able to knock on the tank and tell if there is water in there.

Is the Schrader valve on the bottom of the tank? If it is, and water comes out when you go to check the pressure, the tank should be replaced. These are good ones: https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=therm-x-trol


Is there a valve to isolate the pressure tank to make replacement easier? Else when changing, I would think you would make a mess if you don't drain first, but making a mess combined with speed would mean less deoxygenated water lost.

The air precharge should be the pretty much the same as the cold pressure. But if the air precharge is low, the air will measure pretty much the same as the water pressure. So how would I deal with that? Suppose the cold water pressure is 15 psi, and the water is cold. If the air pressure reads 15, I would add air until the air pressure is 16 psi or more. Then I would let out some air until the air pressure just dropped to 15. Leaving it at 16 would not be bad either. Air will slowly diffuse from the air chamber to the water. So at 16, it would take longer for the air precharge to drop to 14. If you took pressure off the system totally, it would be interesting to know what the air precharge had fallen to. I don't know if that would lose much water.

Recap:
1. Check and fix air precharge
2. If that was OK, try shutting down the input fill valve as Fitter 30 suggested.
3. Consider upgrading from a 2 gallon tank to a 4.4 gallon tank. if space allows.

 

[JD12345]

Hey @Reach4 - I just checked the Schraeder and it's 7.5 PSI. Should I inflate to 15? (Wouldn't this also have the opposite effect of increasing pressure on my boiler?)


Also - The relief valve on my boiler is set to like 40 PSI , which is consistent with the red line on the gauge .... this keeps coming up, my understanding is that it's high for a residential boiler, but that's how this seems to be set up...how uncommon is this?

 

[GrumpyPlumber]

Don't mess with boiler settings, adjusting your home's T-stats won't help either.

Just look at your boiler's static/cold pressure, that right there will tell you a lot.

Your boiler should not be reaching 40 psi, the pressure valve kicks off at 30, this could also mean your gauge is stuck or not working.

 

[JD12345]

I can post some pics but the relief valve is rated to 45 , as is the gauge on the boiler. Is it misinstalled or do I have a funky model, or something else? But both are showing the same thing. Boiler will show 45, relief valve drips. Have seen it.

 

[JD12345]

I can post some pics but the relief valve is rated to 45 , as is the gauge on the boiler. Is it misinstalled or do I have a funky model, or something else? But both are showing the same thing. Boiler will show 45, relief valve drips. Have seen it.

Correction - valve is set to 40, gauge red zone is at 45....I have pics of both if interested.

 

[Reach4]

Hey @Reach4 - I just checked the Schraeder and it's 7.5 PSI. Should I inflate to 15? (Wouldn't this also have the opposite effect of increasing pressure on my boiler?), but that's how this seems to be set up...how uncommon is this?

I would check your air pressure gauge against others. Maybe your tire store would assist in that.

What I don't understand is how you can read 7.5 psi on the air while the water is at 15 psi. But if you dropped the water pressure for taking the reading, and we presume your air pressure gauge reads perfectly,... I was going to write more then, but first lets find out if you dropped the water pressure to measure the air pressure. If the water pressure gauge reads 15 psi and the air pressure gauge says 7.5 psi simultaneously, then at least one of your gauges is off.

 

[JD12345]

I would check your air pressure gauge against others. Maybe your tire store would assist in that.

What I don't understand is how you can read 7.5 psi on the air while the water is at 15 psi. But if you dropped the water pressure for taking the reading, and we presume your air pressure gauge reads perfectly,... I was going to write more then, but first lets find out if you dropped the water pressure to measure the air pressure. If the water pressure gauge reads 15 psi and the air pressure gauge says 7.5 psi simultaneously, then at least one of your gauges is off.

I didn't drop it, but it's possible that the boiler had just shut off. Should I shut the boiler off for a few minutes before taking the reading?

 

[Reach4]

I didn't drop it, but it's possible that the boiler had just shut off. Should I shut the boiler off for a few minutes before taking the reading?

So when you get/got 7.5 psi on the air gauge, what does/did the water pressure gauge say?

If the water pressure gauge reads 15 psi or more, and the air pressure gauge says 7.5 psi simultaneously, and the pump is off, then at least one of your gauges is off.

With the pump off, the pressures will differ due to the altitude difference (0.42 psi per foot). There could be a slight tension on the diaphragm, but that should be small. So a big difference while the circulation pump is off means the gauges have different calibration.

Now what I had not considered before is what if the pump is running? I can see that could explain a difference. But if that is the case, I can say yes, pump that air up to your cold pressure, which may be 15 psi. Yes, your pressure will go up a bit. So I presume you would lose some extra water as a result. But the hope is that you only lose that once at the next big morning warm-up.

 

[JD12345]

haha - i see what you're saying. Let me see if I can find another gauge.

 

[JD12345]

though - after thinking about this, isn't increasing the pressure in the expansion going to increase pressure, not reduce it?

 

[Fitter30]

Don't care what the relief valve setting is need the info on boiler name tag and they have to match.

 

[JD12345]

Don't care what the relief valve setting is need the info on boiler name tag and they have to match.

@Fitter30

Actually - this is on the boiler. Should I assume that max is 50 based on this? (though obviously the fact that it's rated for 40 in Canada makes me think that the right sized relief valve is 40). Am I right about this?

Any thoughts on my pressure problem?

 

[Reach4]

though - after thinking about this, isn't increasing the pressure in the expansion going to increase pressure, not reduce it?

Temporarily. But the matched precharge air will increase the expansion capacity and/or increase tank life.

The Therm-X-Trol tanks have what they call "multi-dome" construction, which limits how much the diaphragm can stretch.

 

[GrumpyPlumber]

"Maximum water temp 250f"

Please, don't.