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# Thread: Leaking Indirect coil causing Boiler Pressure to increase= pop of t+P

1. ## Leaking Indirect coil causing Boiler Pressure to increase= pop of t+P

hi everyone,

Ok so their is a boiler and the PSI is rising and rising until the temperature and pressure releif goes pop. My friend who is a Master plumber thinks its the coil of the indirect has pin whole leak and it allows pressure from the house into the tank. Now he doesn't vocalize much so im not sure how he got to this conclusion. I was looking through threads below just for kicks and saw that a guy was expercing a similar problem with thermal expansion and setting off the pressure relief.

SO i guess my main question is how can you tell Its a leak in the coil i couldn't figure it out, Also how does the house pressure then effect the boiler? I would think if anything would'nt the leak kinda make it like an open system the thermally expanded water could flow into the indirect and then out into the house. Or is this just not feasible due to the pinhole could never handle such a large increase in water volume

2. If you turn off the water to the auto-fill valve to the boiler, and the pressure continues to rise over a few days, that water has to be coming from somewhere, eh? The only likely suspect would be the potable water coil in the indirect, since it's still at the higher pressure. If it doesn't HAVE an auto-fill valve, the experiment is already been done.

Sometimes auto-fill valves leak-through if the valve seats are pitted or get grit in them, which could be another reason for the pressure to rise over time. But if you've turned off the pressure to the potable side of the valve, the heating system's pressure won't continue to rise. As a matter of course I always turn off the feed to the auto-fill after air-purging and pressurizing the system. In the event of a system leak the pressure could then fall, but the boiler makes enough sizzle pop & bang when running at low pressure that it would be noticed well before it became a safety issue. That way the water volume of the leak is also bounded, should a leak occur.

The heating system water is never going to get into the potable through that coil until the pressure on the heating system exceeds that of your potable supply. Since most heating systems are running at well under 20psi, and most potable is running 30psi+, that's just not going to happen if you control the heating system's pressure. Some heating system components aren't designed to operate at potable-type pressures, and you really can't/shouldn't let it get very high. Most are set up in the ~12psi range (static, no pumping), which is plenty for most boilers in 1 & 2 story houses.

3. If shutting off the auto feed does not stop the over pressurizing problem then next shut off the water to the coil over night and see what happens.

4. Dana, Tom thank you, I swear learning about boilers is like learning another language so tricky. Ok i will shut off the manuel autofill and i guesss see if the system de-pressurizes, or goes back down to like 15psi. Dana I cannot beleive i didn't think of the auto filler, I should have realized that they can become pitted and beaten up like everything else. Thanks alot!

5. If it's the autofill, just shutting it would prevent additional water from getting in, but it would do nothing for the water pressure that is already there...you may need to purge a little (it doesn't take much!) to bring the pressure down to the design spec and then see if it stays steady.

6. Thanks jad, i forgot about that i just snuck back to the job and purged it. Im real un familiar with boilers so im looking forward to see if the problem resolves itself monday morning and i plan on reporting back the result.

This stuff makes me think of what dan holhan said about putting a metering device right after the auto fill obv this would be for big big non residential boilers and i think he was refferring to steam boilers.... but on the whole i think for big systems its a good idea that would save alot of headaches if it could be installed cheaply... but then again i know so little that if dan wrote that a boiler works best hanging upside down from the ceiling then Id probably be trying to install one upside down from the ceiling... oh well I can't wait for my copy of modern hydronic heating to get in i think thats gonna really boost my knowledge

7. Once a closed system is filled there is no need for additional water. I have not installed an auto-feed valve on a boiler in the past 20 years or so and never will again. It is a valve that serves no use whatsoever. If the boiler is equipped with a low water cut off (and it damn well should be) I fill the boiler and purge the system once, close the hand feed valve and that's the end of it.

8. Hi guys,
New here with the same issue. 30 psi valve on boiler constantly leaking and Ive replaced it several times.
I have a Weil Mclain Gold series 60 Indirect attached to a Gold CGS boiler. Every year I must purge air from my lines in order to get heat {hot water} to circulate to my attic {second floor} in the air handler.
I have just recently replaced both expansion tanks as they were filled with water. I have an autofeed, 12psi, which I've also replaced.
The domestic water coming into my home was 90psi. On the recommendation of plumbers I work with, Im an electrician, they strongly suggested I put a pressure regulator at the water main and bring it down to 60psi. I have done so. Having a friend over recently who has had the same issue noticed my dripping Pressure Relief Valve, told me he had the same issue and his master plumber resolved it by replacing his Indirect Heater.
Do I have other issues here or should I look at replacing my 13 year old Gold Series 60, 48 Gallon.
I have also installed a pressure gauge at the Water Heater which is a constant 60. The new pressure gauge I've installed on the boiler never exceeds 20psi.
Thanks
Louis

9. The heat exchanger in the indirect may have a pinhole leak in it allowing the potable water to leak into the lower pressure boiler loop. If that's the case, you need to replace the indirect.

10. That's pretty easy to diagnose too. Turn off the water at the autofill, isolating the heating system from the water main. If the water pressure on the heating system continues to creep up over several days (not just when firing), it can only be coming from a leak from the potable the heating system side of the indirect. But if it never exceeds 20psi as reported, it's probably not leaking.

Sealed heating systems would also not need annual air purging. The only way for air to get into a pressurized system is if it's leaking a lot of water somewhere, and the auto-fill water has a lot of dissolved gases. If that's what is happening, the heating system pressure would DROP in the days/weeks after you've turned the fill water completely off.

11. This sounds interesting. I just bought a new hot water heater and was installing it this coming weekend. My current one is Lifetime with Weil McLain. They will reimburse me when they get the old one back.
The pressure at the boiler never exceeds 20. I will tonight turn off the Auto-fill and check it in a day or 2.
Is it safe to leave the Auto-fill off that long?

12. There is NO requirement to have an autofill valve at all. If the boiler system is working properly, you fill it once and never need to deal with it again. SO, yes, you can leave the autofill shutoff closed as long as you want. What would happen if you have a leak is that it would mask the problem. If there is a leak, at some point, the boiler will shut down if it doesn't have enough water.

13. What Jim said- autofill valves are "solution-problems", designed to keep the system from running low on water in the event of slow leaks, but creating overpressure problems when they fail, and in the event of a sudden catastrophic leaks on the system they create a flood. If your heating system starts running low on pressure you'll figure it out long before it presents a hazard- the sizzle & bang from the boiler gets progressively louder as the micro-boil on the heat exchangers turn ever more macro.

I typically only check the pressure on the system at the beginning of the heating system or whenever I've broken open the system to monkey with the radiation or something an have purged air, re-filled, etc.

14. OK, Auto-fill off now 2 days and I've noticed, while making Hot Water, that the boiler pressure appears to Max out at 28 PSI. The domestic pressure at the hot water inlet is 68 PSI. I have purchased the new hot water heater but am waiting to be sure its the real problem before spending \$1300 for nothing. The last thing I want is for Well McCain to tell me there is nothing wrong with it and will not reimburse me.
This forum, like others I belong to, is extremely helpful. Thank you ALL for your help!

15. 28psi is bumping pretty close on 30psi. Sounds like the expansion tank on the heating system may be marginally sized or not correctly pre-charged. You should set the system at 12psi when the boiler is cold.

What type of heat emitters and piping do you have (other than the hydro-air coil on the second floor)? Big high-volume radiators need much bigger expansion tanks than fin-tube baseboard, due to the high volume. If the original expansion tank was marginally sized and failed, this one will too.

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