Potterton PERFOMA 30 HE boiler pressure dropping 0.1 bar per day

27 Dec 2020
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United Kingdom

I have a 15 year old Potterton Combi Performa HE30 and the first 10 years are fine with no visible need to top up bar the annual service and then over the next 5 years, I have noticed I need to top up the pressure with increasing frequency starting with twice a year, then 4 times a year, etc over and above the annual boiler service. Of late, I need to top up the pressure during winter like once a week to move it from 0.8 to 1.5. So it is like dropping 0.1 bar a day on average. I do notice that the drop is more if the heating is on than now with the heating off during summer but still dropping none the less like 0.5 bar a day. I had a boiler guy came to check and he said, everything with the boiler is fine. He was pretty sure my 15 year old boiler is not leaking. He checked the PRV, checked and pumped the expansion vessel, and drained the condensate as he isolated the pipework system and the boiler. He came to the conclusion that there must be a leak in the pipework - radiator system. It is a nightmare to rip up the floor boards and uncover pipes in the kitchen and before I do that, I did think of getting a thermal camera but it seems that pipes in the void (rather than buried in the ground) will not show much thermal disturbances to identify a leak. So maybe it is not a good idea to rent a thermal camera.

I am of two minds. Take a chance and get a new boiler (since the Potterton is now 15 years old) and maybe the leak is in the boiler and got burnt off by the pilot flame. Or do a simple experiment and that is since it is summer now, turn off the inflow and outflow valves (first and last pipes at the bottom of the Combi) to the central system pipework, having topped up the pressure to 1.5 and bled all radiators and leave the system for 2 weeks. I assume if the leak is with the ground pipes, then after two weeks, when I turn the two valves back on, the pressure in the gauge will show a sudden drop. But if the leak is in the boiler, then the boiler pressure will still drop everyday despite me turning the inflow and outflow valves of the gas heating system.. Will the turning off the valves be able to sustain the difference in pressure between a leaking pipe system and the pressure in the boiler ?? Will the above experiment prove that the leak is in the boiler or in the pipework? Or maybe just buy a new boiler and hope that the pipework/radiator system is fine.

The pipework must be over 35 years and current radiators were put in 15 years ago.

Thanks for your help.
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Yes ,isolate the flow and return at the boiler. Assuming the isolation valves do fully close as they should ,pressure loss would indicate it's from the boiler. No loss until isolation valves are opened would indicate it's lost on the system side.
after 5 days with the flow and return valves turned OFF to the radiators/system, the boiler pressure continues to show a drop in pressure over time like 0.3 bar over the 5 days. And when I turned the two valves back ON, there was no effect to the pressure reading. So my guess is that the leak must be in my boiler but I see not water and the gas engineer was so adamant that the leak is in the system. Maybe I should just replace the 15 year old boiler to save some money on my gas bill and perhaps to 'fix the leak' hoping that the leak is not in the system side. Any view or further tests? thanks in advance
There is the possibility that the isolation valves are not fully closing, and there may be a leak on the system.
To be certain that the boiler is the source of the loss ,you would need to sever ,and cap off the system from the boiler. Then
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There is the possibility that the isolation valves are not fully closing, and there may be a leak on the system.
To be certain that the boiler is the source of the loss ,you would need to sever ,and cap off the system from the boiler. Then repeat the test.
if its on the boiler then it will more than likely be the secondary heat exchanger leaking they are anything up to 300 quid new and can be a bit of a nuisance to fit , Disconnect the condense pipe on right hand side and see if this drips that will confirm it . if it is leaking then i would just live with it
It seems that the pressure drops when I use the boiler to heat up water for my bath but if I don't have bath that day, then the drop in pressure is much less. Looks like when the boiler is heating water for my bath, the leak is worse and so it also proves that the radiator and pipe system is not leaking as the Central heating is turned off now. So I guess even though I cannot see water dripping from the boiler, the leak is in the boiler and is worse when the heating is turned on to give hot water to my bath tub.
To Gas112, thanks for your advice.. but the gas engineer has disconnected the condense pipe and said that it did not drip and so he was very sure that the leak is in the System. But I still suspect the leak is in the boiler somehow as it is 15 years old.. and I think I am going to get a new boiler anyway now that gas is so expensive and inflation is going to hit boiler installation and prices ..and my boiler is coming to end of life.. thinking of going for the Worcester Bosch Greenstar 4000 25kW.. any comments? thanks in advance.
worcester have good marketing to make their expensive boilers look a lot better than they are they are definitely not the installers choice .
you are not going to save a great deal of money on gas from around 88% efficient to around 92% and that is only for a short time will boiler heats up after system is hot they are basically the same efficiency.
Also by dropping to a 25 from a 30 your hot water delivery will be reduced .
A baxi 630 7 year warranty will fit straight to your existing pipework with minimal alteration basically 5 sockets and slight alteration to blow off and condense and use the same flue hole

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