CH Goes Over Pressure and DHW Cuts Out

[holla]

Hi. Our Potterton Performa 24 was working, seemingly, without any issues for the 3 years we've been in this house. My other half drained the CH and moved the radiator in one of the bedrooms before repressurising. Since then the central heating pressure slowly creeps up and within 10 minutes or so it's at 3 bar. I wasn't paying attention once and caught it at nearly 3.5 bar. I've checked when it was slightly over 3 and water slowly drips out of the overflow outside at a rate of about one drip per second, if not slightly slower.

It was like this for a few days before we bled the radiators again and now when we run the hot tap the water will work for about a minute and then the flame goes out for 10 seconds or so and reignites and the cycle continues. The water doesn't get much chance to get anything other than warm. There is a rumbling/groaning sound that lasts for 3 seconds or so either just before or just after the boiler going going off, I can't recall which. If we run the tap slowly the groaning sound is not as loud but still as periodic, the water is hotter and it doesn't shut off.

What do you think might be wrong please? Pressure related or something else has gone coincidentally.

EDIT: Sometimes it shuts off when running tap slower.

 

[Terrywookfit]

Check filling loop not passing.
Check EV charge.
Check PHE.

 

[holla]

Thanks for the reply. The manual says to access the expansion vessel the boiler needs to be removed from the wall so that's an option for the likes of me I'm afraid. The plate heat exchange looks like it may be tricky to remove also but I have seen something online that suggests checking the safety thermostat resistance which is showing 5 ohms instead of the recommended 11-13 thousand. As they're only a few quid I'll pick one up tomorrow and try that.

If that doesn't do anything I'll investigate how to remove the PHE.

 

[ianmcd]

The manual says to access the expansion vessel the boiler needs to be removed from the wall

No it doesnt, it says that to replace the expansion vessel then the boiler needs to be removed from the wall, not the same thing.

safety thermostat resistance which is showing 5 ohms instead of the recommended 11-13 thousand. As they're only a few quid I'll pick one up tomorrow and try that.

save your money you have got that completely wrong

 

[holla]

Fair enough, I don't know what I'm doing, as you can tell. I will look into removing the phe tomorrow. Any tips for removing it on this particular boiler? Out of interest, is the thermostat resistance totally wrong then? How would I check it? Another site appeared to confirm some resistances for it when it's a certain temperatures. Would the thermostat being faulty just not cause those symptoms?

EDIT: Also, how exactly to check the ev?

 

[AGAS]

safety thermostat resistance which is showing 5 ohms instead of the recommended 11-13 thousand. As they're only a few quid I'll pick one up tomorrow and try that.

would like to hear where you got that from , its an NTC if thats what your referring to

 

[holla]

I've just checked the thing above it on the same pipe, that the manual refers to as the temperature sensor and that's 10,000 ohms so it looks like I got the wrong component. The first source was from

and the second was a website that I visited but there's been so many that I now can't recall which one it was. Basically, I'd got the wrong thing :-/

 

[holla]

What does NTC stand for?

 

[holla]

I've checked the ev and it had a fart's worth of air in it. Do I just drain some water off the boiler to reduce pressure and then pump 7 psi into the ev? Then top up water back to .5 bar?

 

[AGAS]

I've checked the ev and it had a fart's worth of air in it. Do I just drain some water off the boiler to reduce pressure and then pump 7 psi into the ev? Then top

HERE

 

[holla]

I took it upon myself to have a go before your reply and drained the boiler to nearly 0, then isolated the water and pumped until the boiler was at .5 bar. Checked with my gauge and it was 7.5 psi so all good. I enabled the water again and ran the tap... It went for about a minute and got hotter than it has been but not what you'd really call hot, then the boiler turned back off again. It did fix the noise though so now it's quiet again and no groaning.

Looks like the phe is next. I'm a bit hesitant with water pipes as I've had unpleasant experiences in the past with leaks. Do I need new washers or anything if I do get it off?

And thanks for the continued help!

 

[AGAS]

I took it upon myself to have a go before your reply and drained the boiler to nearly 0, then isolated the water and pumped until the boiler was at .5 bar. Checked with my gauge and it was 7.5 psi so all good

really!!

It did fix the noise though so now it's quiet again and no groaning.

really

try turning the hw temp control down to say half way and back to full a few times and see what happen to the flame each time after turning ?

 

[AGAS]

[

 

[ianmcd]

I took it upon myself to have a go before your reply and drained the boiler to nearly 0, then isolated the water and pumped until the boiler was at .5 bar. Checked with my gauge and it was 7.5 psi so all good. I enabled the water again and ran the tap... It went for about a minute and got hotter than it has been but not what you'd really call hot, then the boiler turned back off again. It did fix the noise though so now it's quiet again and no groaning.

Looks like the phe is next. I'm a bit hesitant with water pipes as I've had unpleasant experiences in the past with leaks. Do I need new washers or anything if I do get it off?

And thanks for the continued help!

You are not reading what you should do, you MUST leave a drain point open when you are pumping the vessel back up, not maybe, you MUST, the water that is trapped inside the vessel has to be removed before you can start to pressurise the vessel then you close the drain point and add water to pressurise the system to between 1 and 1.5Bar

 

[holla]

I misunderstood. I have drained the boiler via the drain cock as per the linked page, closed it off again and pumped ev to 7.5psi and then drained again. I did that about 5 5-6 times and about three quarters of a bucket of water had been removed and then inflating the ev to 7.5 and trying to drain it removes only a tiny bit of water. This was my interpretation of the instructions at least. It has not solved the issue of hot water though; It ran for about a minute and then stopped. If I then try it again straight after it only burns for about 5-10 seconds before stopping. Altering the temperature control for the hw on the boiler doesn't appear to change the burner flame as it's running.