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

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.

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.

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!

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.

Thanks jad, i forgot about that :o 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

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.