boiler pressure

[ssb1973]

Hi all,

I have a Vaillant thermocompact 628E, and the pressure was near to zero, so I filled it from the filling loop to around the number 1. Recently, I've noticed when the radiators come on in the morning, the pressure is over the red line after the number 3. I used the pressure relief valve to reduce the pressure, and since have not filled from the filling loop. But the pressure still goes to past the maximum.

I thought this may be due to the filling loop not tightened, but it seems to be fine, and I can't hear any water passing through the filling loop.

This morning, I noticed the pressure past 3 again, and tried turning the pressure relief valve but it wouldn't turn, it just kept spinning around. I'm thinking perhaps it's due to the cold weather outside the outside pipe could be possibly have frozen water in there or maybe the relief valve is emptying automatically.

My main concern is the pressure valve going past the maximum even though no new water is added from the filling loop. Has anyone come across this type of behaviour on their boiler before?

 

[sooey]

If the filling loop isn't passing water when it shouldn't be, it will be the expansion vessel. If you look in the sticky at the top of the page there is an explanation.

 

[ianmcd]

This could be dangerous if the PRV outlet pipe has frozen over you could burst something inside your boiler, if you havent been constantly topping the pressure up and it has been passing to outside then the filling loop valve is passing, you need to rectify this immediately, you shouldnt be using the PRV to reduce the pressure manually you may get dirt on the valve seat and it will constantly leak

 

[ssb1973]

Thanks for the responses. I don't think the PRV was frozen, as I can see water coming out of the outside pipe no problem, and the water has been coming out when the pressure is high automatically.

We did have an issue yesterday where there was a failure code f.22 which meant low water pressure according to the manual, I topped up the water to around the number 1 from the filling loop, and reset the boiler to get it to ignite. All was well, but the pressure still goes to around 3 when the boiler is heating, and as a result water is always passing through the PRV when the pressure is high, but it is doing it quite frequently.

 

[CBF]

the EV needs repressurising or replacing & prob the prv as well now

 

[ssb1973]

I've left the combi boiler as is and have not refilled from the filling loop since, and the boiler pressure stays around maximum 3. The PRV outlet pipe is always dripping water outside when the heating is on, which is at cost, as we have a water meter.

We did have one of our upstairs rads being cold from the top part, so I bled the rad, and released some pressure, the rad is heating ok now. Bleeding the rad reduced the pressure on the combi to 2, but it climbed back to 3 again later.

Is there anything that I could do DIY, to stop the PRV leaking water when the heating is on?

 

[hazetimesfive]

not really, it needs fixing properly, you will have lost all your inhibitor by now and thats not good.

 

[ssb1973]

So would I need a PRV replacement based on the symptoms?

 

[captain_pugwash]

The PRV does sound as if it is leaking - in which case it does need replacing as you will forever be topping up the pressure and it can drop off so low as to cause the boiler to fail to start. Does also sound like you need to fix the cause first though - if you are seeing 3 bar the whole time then the PRV will generally activate at this level - and you will end up ruining a new PRV as once they have activated they rarely seem to seal again. From what you have described it does sound like an expansion vessel issue - this is designed to take up the extra pressure when the water heats up and expands. If this is not working then you can find the PRV activating all the time.
Most EV's have a tyre like valve that you can attach a tyre pump and pressure gauge to. If it is flat you can pump it up - it's a bit like a hot water bottle.

You will need to find out from the boiler manual what pressure it should be (when cold).

If it is flat then just pump it up. If it goes flat again then it will need replacing.

 

[ssb1973]

Many thanks Captain Pugwash, I will give that a try, the normal pressure should be around 1.5 bar. The pressure is currently at 3, and doesn't require topping up after the PRV leaks, it just always goes back to 3 eventually even when I reduce the pressure using the PRV.

Should I pump up the expansion vessel the system is cold and switched off, and should I reduce the pressure before pumping?

Many thanks.

 

[ssb1973]

Hi,

I got it fixed through my home emergency cover when the outside pipe froze, they called an engineer from Vaillant. He replaced the PRV and also a couple of other valves, and pumped up the expansion vessel. All been working fine now for a few months.