Combi Boiler Pressure Too High *When On*

mcompton69

We were lucky enough to inherit a Worcester boiler with our house (28i Junior to be precise). Never had a problem with it, or the CH system.

Bled a top of house radiator sunday night as the top wasnt hot, no probs there, didnt check the boiler pressure afterwards though, and Monday morning the missus had hold/cold shower as the boiler didnt work properly due to low pressure (the noise of the air in system woke me up).

So carefully topped up the system to 1 bar, no problems. Came home from work 9 hours later, same pressure of 1 bar (so i dont think the mains valve is open at all).

However, when the system is on the pressure rises to 3 bar (when it red lines), i dont recall it ever getting that high before when running.

Q1) Should I be concerned about this? Do i need to do anything?
Q2) Could it cause damage to the boiler?

I mention the boiler make/model as i am sure that there will be a pressure release valve, and i can see a plastic pipe leading to the shower waste water pipe, so it shouldn't explode! But I want to make sure...

Thanks for any advice and tips people, you could save me a significant plumber call out charge with your advice!

worriedindebt

I'm not a plumber/engineer but have had combi boilers for years so thought I'd offer my help (which is only for info, maybe a qualified person can verify)

Firstly I have noticed before that the pressure does rise when the heating is on though to rise by 2 bar does seem a bit much?

Secondly are you sure the valves were closed fully when you topped up? I've done this in the past and the pressure crept up.

Thirdly I once had a problem where the pressure rose to nearly the maximum, I was worried sick. The engineer that came told me I needn't have worried as there is a safety valve that will blow in event of a massive rise in pressure and the boiler won't blow up.

In summary, check the valve is definitely turned off and not topping up. Then don't worry too much, and if it gets too high then maybe call an engineer.

Hope that helps you

traineepensioner

I'm NOT a heating engineer and I'm sure one will be along shortly....If your pressure builds up from 1 bar to over 3 bar when you first turn on the heating you may be losing water through the pressure release valve. Usually discharged via a 15mm copper pipe outside. (If it's difficult to tell you could try fitting a balloon over the pipe to see if it collects any water)

I had this problem and it turned out to be that the expansion vessel required repressurising (easy fix):)

good luck

Ectophile

Q1) Yes, you should be concerned.
Q2) It certainly won't be doing any good. In the end, the pressure relief valve may fail.

It's probably the expansion vessel that's failed. Depending on how it's failed, it either needs re-pressurising or replacing.

Lgas

Expansion vessel probably needs to be pumped up again - get a gas safe engineer out to do this. Hopefully it doesn't need replacing! You don't want it to cause the pressure relief valve to open as they often don't re-seat properly, you can always release some pressure from a rad in the meantime. Did you check the pressure before you bled the rad? It may have been low already if the PRV has opened due to high pressure and you haven't noticed.

cyclonebri1

I'd like to pop my own question in here as it's similar.

I have a Glow Worm Swiftflow 100e combi, it's now about 17 years old and has been pretty much faultless in that time. I have been expecting to have to change it for some years now.

I set the static pressure to 1bar and it rises to 2 bar in use, has always been like that. Only needed water adding about every 18months when it dropped out under low pressure.

Something has changed, pressure is down to about 0.25bar and the system still runs, increases to 3 bar when in service.

Is it the end of the road?

Ruski

Pressure vessel failure/re-pressurising.

I'll leave it you you what to do next Bri.

HTH

Russ

cyclonebri1

Ruski wrote: »

Pressure vessel failure/re-pressurising.

I'll leave it you you what to do next Bri.

HTH

Russ

Yeah, I'm guessing something similar but other than the basics I'm no boiler expert.
Haven't re pressurised for about a year, only just noticed it's under the point were it shouldn't function, so don't want to top it up and let it go off the scale at this time of year.

It won't get repaired, not at that age, just don't want a complete failure until summer;);)

They always say the cheapest boiler is the 1 you have now, that's why for the last 5 years I've been saying "I really ought to change it thios summer, but.......:money:" :D

southcoastrgi

it's not a repair as such cy if the ev just needs re-pressurising, an hour for an engineer if the isolation valves under the boiler turn off, if they don't then the system will need to be drained because if you use the prv to release the pressure it will prob need replacing after as they very rairly re-seal

JohnB47

This thread made me curious, so I searched and found this:


http://www.lovekin.net/system-pressure.html