Boiler dropping pressure

Mr_Mister

Hi
I have a Vallaint Ecofit combi boiler that has been dropping pressure every week for the last 3 months.
I've had Vaillant engineers replaced the Expansion Vessel and Pressure Relief Valve recently under warranty but that did not make much difference.
I have also checked all radiators and visible pipes and cannot find any obvious leaks. 
Does anyone else have any suggestions on what else to investigate?
Thanks

Bendy_House

The next standard test is to isolate the boiler from the radiators, so you can narrow it down to either being within the boiler, or it being in the pipework and rads. But this will require shutting off the boiler for the duration of the test, and the pressure loss would have to be noticeable.

Ie - if it takes 2 days to notice a drop, then it'll take two days to carry out this test...

Essentially, it involves pressurising the boiler to a recorded figure - say 1.5bar. The boiler is shut down, and the valves on the Flow and Return are closed. After the required time, if the pressure has still dropped, then it's from within the boiler. If the pressure remains steady but drops the instant one of the valves is opened, then the loss is in the external pipework/rads.

Bendy_House

What does the pressure gauge read when the boiler is cold, and then as it heats up? What is the highest it goes to?

Mr_Mister

Bendy_House said:

The next standard test is to isolate the boiler from the radiators, so you can narrow it down to either being within the boiler, or it being in the pipework and rads. But this will require shutting off the boiler for the duration of the test, and the pressure loss would have to be noticeable.

Ie - if it takes 2 days to notice a drop, then it'll take two days to carry out this test...

Essentially, it involves pressurising the boiler to a recorded figure - say 1.5bar. The boiler is shut down, and the valves on the Flow and Return are closed. After the required time, if the pressure has still dropped, then it's from within the boiler. If the pressure remains steady but drops the instant one of the valves is opened, then the loss is in the external pipework/rads.

I suspect it could be a leak in the pipework hidden somewhere under the floors or walls but can Gas Safety Engineers locate the leak without ripping up all the floor boards etc? 

Mr_Mister

Bendy_House said:

What does the pressure gauge read when the boiler is cold, and then as it heats up? What is the highest it goes to?

I notice it usually drops when the boiler is not working. 
It drops to just above 1.0. 
I usually repressurise it to 1.3-1.5 and it stay like that for days but then suddenly one day it drops to 1.0 or lower

Bendy_House

Does it vary much between the boiler being cold and hot?

Always worth checking the most common issue (that you've just had fixed...) as it's easy to do - rubber-band a plastic bag over the end of the 15mm copper discharge pipe outside. You want to be able to discount his first.

badger09

Mr_Mister said:

Bendy_House said:

The next standard test is to isolate the boiler from the radiators, so you can narrow it down to either being within the boiler, or it being in the pipework and rads. But this will require shutting off the boiler for the duration of the test, and the pressure loss would have to be noticeable.

Ie - if it takes 2 days to notice a drop, then it'll take two days to carry out this test...

Essentially, it involves pressurising the boiler to a recorded figure - say 1.5bar. The boiler is shut down, and the valves on the Flow and Return are closed. After the required time, if the pressure has still dropped, then it's from within the boiler. If the pressure remains steady but drops the instant one of the valves is opened, then the loss is in the external pipework/rads.

I suspect it could be a leak in the pipework hidden somewhere under the floors or walls but can Gas Safety Engineers locate the leak without ripping up all the floor boards etc? 

I really hope its not a leak under your flooring, especially if like us, yours in concrete and ceramic tiles in several rooms. I'll keep an eye on this thread & post more once you've eliminated the boiler being at fault.

FYI, the Gas Safe Engineer will not be able to detect under floor leaks.

Mr_Mister

Bendy_House said:

Does it vary much between the boiler being cold and hot?

Always worth checking the most common issue (that you've just had fixed...) as it's easy to do - rubber-band a plastic bag over the end of the 15mm copper discharge pipe outside. You want to be able to discount his first.

I've done what you have said and placed a bag over the pipe a few days ago.
So far the bag is empty and the pressure has stayed at 1.5.
It does normally take a week for it to drop and will report back when it does. 

Bendy_House

Thanks for the update.

A quick dump like that (matron!) usually indicates a system whose pressure has gone too high and the water is released in one go via the safety discharge pipe. So it'll be interesting to see if you catch anything in that bag when the next loss occurs.

Meanwhile, could you keep an eye on the system pressure, and see if it varies much as it all gets up to max heat, with rads piping 'ot?

Mr_Mister

Bendy_House said:

Thanks for the update.

A quick dump like that (matron!) usually indicates a system whose pressure has gone too high and the water is released in one go via the safety discharge pipe. So it'll be interesting to see if you catch anything in that bag when the next loss occurs.

Meanwhile, could you keep an eye on the system pressure, and see if it varies much as it all gets up to max heat, with rads piping 'ot?

Hi the pressure dropped to 1.0 this morning and it has been steady at around 1.5 for many days. 
I've topped it up now as the tap water appeared warm rather than hot and no doubt the pressure will drop below 1.
I checked the bag and there was no sign of any water drops. 
What do I do next? 
Thanks

Bendy_House

1 bar is perfectly fine, and wouldn't top it up again unless it goes to 0.8 or below. Your boiler should have been working fine at 1 bar, so I don't understand the water feeling only warm - I suspect you didn't let it run for long enough, or ran it at too fast a rate.

Before doing anything else, can you answer, please - does the pressure vary as the boiler heats up the CH?