Laars Endurance boiler over pressurizing

16 Apr 2019
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United States
Hello, first time on this page but I’ll do my best to explain my issue.

It all started when my boiler malfunctioned, ended up being the blower, the flame tube and the igniter.

After this was fixed by a professional after the system pressurized it started leaking out of the pressure relief, no big deal just thought it was air bound, so we relieved the pressure and it was fine....till a few hours later when it over pressurized again.

Now my uncle was a plumber and he came over and said that it was probably the water inlet valve and the back flow valve, i agreed and we replaced both and again, it was fine for a few hours and then over pressurized again.

Looked through some forums and found it could be a faulty expansion tank so i bought one and replaced and also figured it would be good to change the relief valve at the same time so i did and everything seemed great, we got the air out and the expansion tank and air bleeder on top was working great, until a few hours later and it over pressurized again.

I tried shutting the main valve for the water inlet off and let that sit over night after i drained and pressurized the system to the correct psi (15-20psi) and woke up this morning to again an over pressurized system and it was dropping yet again.

I’m at my wits end, it’s impossible to get my uncle out so I’m trying to figure this out but I’m lost at what more could there be to replace that would pressurize the system.

Any help is much appreciated
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How is your expansion vessel connected to the system ? is it a flexible hose or is it a fixed pipe, these are called communication hose/pipe, if there is a blockage here then in effect your expansion vessel is non effective, if this is all clear turn off the cold water inlet again but disconnect and cap it and see what happens, if this valve is passing and you have a pinhole in the DHW heat exchanger that would also cause the over pressurization
It’s a fixed pipe but I guess i should of mentioned the issues have been on the home heating side, would the DHW still have an effect on that?
yes the way your DHW heats up, the heat exchanger is a series of plates that alternate carrying system water the DHW then system water and so on, so within that heat exchanger you have both mains water and system water, the dont actually meet they are separated but it is possible for a pin hole to happen in the mains plates and this then passes into the primary water causing the over pressure that you are experiencing, but if you physically disconnect the cold water inlet valve and physically disconnect the filling loop and leave them overnight with the heating on you will know if it is an expansion or an overfilling problem
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Alright, I’ll try to do them both and see what happens. Is there any reason why this would just fail after getting the blower replaced?
Sorry I called it a filling loop, on your boiler it is called an auto fill valve, check this and make sure it is not passing as this would also cause it, cant thing of anything that replacing the fan could cause this (blower as you call it) however you did say that the system was re-pressurized after this repair, cant think why it had to be drained , but in order to repressurise then the auto fill valve would have to let water in and its possible that the valve seating has not sealed properly when the pressure reached 1.2 Bar
I replaced the auto fill valve and even shut that loop off last night to see if it was still pushing water through and it was at 15psi last night before i went to bed, woke up this morning and it was 30psi with that closed and only reason system was re pressurized after the blower was replaced was because when the technician first looked at it the pressure was at 40psi and he decided to drain some to relieve that
well in that case it was already over pressurising before the tech touched it, as an ultimate test if you can do with the inconvenience over night, shut the cold water main off to the whole house and leave the heating on, if the pressure remains constant then you have a passing issue somewhere, if it has went up again then its an expansion problem, are you sure that the expansion vessel is big enough for your system ? as a short rule of thumb its 1L expansion per radiator but that is just a rough calculation
I just used the standard size i believe a #30 i only have 4 radiators. The expansion tank was the same as the one that was previously in there but i can try shutting off the hot water today when i get home and see if anything happens
not the hot water the cold water inlet to the house, and if you only have 4 rads the expansion vessel will be large enough, by closing the cold water inlet to the house you are ensuring that mains water is not getting into the primary water somewhere

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