Boiler pressure going down. Help?!?

[Blunet600]

Are there any boiler experts on here? My boiler keeps losing pressure. I re-pressurize it and in a day or two it will have drop below the recommended pressure range.
I've read on Google some things it could be but don't know what I'm looking at. Someone mentioned a overpressure valve. Any help would be appreciated.
I'll load up some pictures of the set up.
Thank you.
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[LustyLew]

It could be a PRV valve leaking. There should be a small pipe going to the outside of the property, if the PRV is leaking you should notice a drip or evidence of moisture. If the PRV is not showing signs of leaking, don't fiddle with it, I hear that once activated they need to be replaced as they never seal properly afterwards.

You should also check all pipework for any small leaks.

My sealed system was losing pressure over 3-4 days, discovered a slightly leaky rad valve in the bathroom.
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[Rogerborg]

Fernox F4 leak sealer has sealed my system up tight and not[*] caused any assplosions or pump failure.

[*] yet
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[scorps]

I had a miniscule leak in one of the threads on a pipe to a radiator which did this. I tightened it and it sorted the problem, start with the simple things first.
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[chris-red]

[arry]

Almost certainly a leak. Flow switches and valves in the combi itself can leak so stick a tray underneath the boiler and see if you catch any water. These leaking is a more serious problem than a thermo valve on a tad

[MarJay]

I had like that and it was a piece of scale caught in the pressure release valve. The plumber replaced the PRV and it was then fine.
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[Wonko The Sane]

I'm guessing you've bled and checked bleed screws on radiators already?

As already said, check radiators and connections you can get at to see if there are any slight leaks
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[Raffles]

A quick examination of the expansion vessel may yield the answer to your problem.
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[DrDonnyBrago]

Pressure release valve and/or expansion chamber broken.

My last house had a dodgy expansion chamber, the rubber bladder had split and over time the air in it dissolved into the water. As such, no capacity to allow the hot water to expand, the excess was being dumped every time the heating was run and the pressure dropped over time.

[Going]

[Andy_Pagin]

Having experienced the same problem I'd suspect a leak somewhere inside the boiler casing. Take the panels off and have a good nose around. The geniuses who design these things usually place the uber-expensive circuit boards more or less in line with any water leakage, so ignoring it could get very expensive.
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[janner_10]

Turn heating on and walk around house and check for leaks first.
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[Blunet600]

These are the pics of my system underneath the boiler. I live in a top floor flat...
I will do a run around on my day off to check for leaks.

Thank you for your help so far. Once i've worked out where all these different valves are i will check them too.
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[Andy_Pagin]

At a glance that pipework looks ok. Your next job should be to take the casing off the combi unit and nose around with a torch and ideally an inspection mirror looking for any signs of limescale build up, find any and that's where the leak is. It doesn't take a huge leak to lose pressure, the whole point of a combi is that it only holds the bare minimum amount of water.
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[spnorm]

It's probably a split diaphragm in the overflow tank. We had the same problem and the plumber fitted an external overflow tank for about £70

[bladerunner]

No one has mentioned the first place to check after your pipes and radiators and that's your AAV that's automatic air valve if you have one fitted. Usually looks like a brass float valve with a tire valve sticking out the top ( may have a loosely fitted plastic cap on the valve). Its purpose in life is to vent any air from the system and are prone to failure if limescale or dirt gets in the seal and will usually be no more than a slight fluid leak at worst. They are either in the boiler or on the heating hot water feed pipes in your attic.Prv's don't usually give issues unless venting due to over pressure or opened manually which also means dirt in the seal but can usually be fixed by pressurising the system and opening and closing aggressively which flushes debris from the seal. Pressure vessel failure is also common and will initially show pressure loss but then when the system is pressurized again the pressure will go up when warm as there is no longer room for expansion, this is usually checked by a quick press of the valve....if water and not air is released then its shot....bear in mind if you release to much air you'll destroy the bladder anyhow and it should be slightly pressurised to work......oh sod it just call a heating engineer
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[mudcow007]

Im pretty sure we have a leak too, if we dont have the heating on for months at a time, it drops from 1bar to around half - ish

just refill using the loop an all is good for a few months.

Have you tried bleeding your radiators?

[J4mes]

I had a leak for about 3 years that I could never find - until someone pointed out that my kickspace heater in my kitchen was fed by the boiler. I always thought it was electric so I never used it.

Took the lower panel off my cupboards and there was the pool of water!

[Blunet600]

I re-pressurised the boiler yesterday up to around 2.5. Checked it this morning and its at 1!
So i re-pressurised it today to 3 bars on the line and the heating is off, checked it just now and its already dropping....
i took the casing off and aside from having no idea what im looking at i couldn't see anything obviously wrong. will post the pics once i have uploaded them.
Any ideas?

Ive checked the radiators and not found any leaks.

cheers guys.
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[J4mes]

Does the manual say to pressure it that high? The three boilers I've had were pressured to 1.5-1.7bar

[Bikeless]

So have you checked it's not dripping from the pressure relief valve pipe outside?
Odds on the pressure vessel is knackered aswell.

[bugeye_bob]

When was the boiler last serviced ?

[LustyLew]

Have you actually checked anything that has been recommended here?

If you're having trouble checking something as simple as a leak, please get a professional before you blow yourself up. pressurising your system to 3 bar is not good.
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[calyx]

Here is a check list for you:

Before checking for leaks, make sure your pressurization tank is 1.2 bars then pressurize the system to whatever your mains pressure can achieve. Your system is rated for at least 10 bars. Don't worry just go for it. Run the system at minimum heat. Make sure your hands are bone dry and check for leaks with the help of a kitchen towel. Now check;

-every single coupling, elbow, tee.
-radiator valves
-bleeding valves
-relief valve and its outlet.
-pressurization tank
-every single weird looking thingy inside the boiler case.

no luck?
close all radiator valves. run the system. it will struggle, don't worry keep it running for 8 hours. pressure still dropping? your radiators are not leaking.
focus on the pipes and the boiler.
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