Boiler pressure

tony3619

So I just tested my boiler and heating ready for the winter (not that I'll be able to afford it!) And Ive noticed the pressure gauge is going higher than before. 

Normally I pressurise to 1.3/1.4 and it will normally stay the same in operation or maybe get to 1.5. 

It's now shooting up to just 2 / 2.1 when in operation. Could this be due to the higher temp outside? (It being 25c and not 13c) or does it sound like a PRV problem?

The heating hasn't been used in 5 months and the pressure never goes into the red 2.5-3.5

macman

Make and model would help. Condensing combi?
Is the PRV venting water outside? More likely to be a problem with the EV if the pressure is rising Nothing to do with the outside temp, it's a sealed system.
You imply that the boiler has not been used at all for 5 months, so how do you heat your hot water?

jonnydeppiwish!

The water pressure will rise when it’s in operation - that’s normal.

tony3619

macman said:

Make and model would help. Condensing combi?
Is the PRV venting water outside?
More likely to be a problem with the EV if the pressure is rising.
Nothing to do with the outside temp, it's a sealed system.

It's a combi potterton promax. No sign of PRV venting. I do have an on going issue of the pressure dropping over 3-4 months if that gives any clues? 

macman

Pressure drop on a combi is invariably either the PRV venting, EV faulty, or a leak on the CH circuit. But the pressure rise you refer to points to the EV.
When was it last serviced?

tony3619

macman said:

Pressure drop on a combi is invariably either the PRV venting, EV faulty, or a leak on the CH circuit. But the pressure rise you refer to points to the EV.
When was it last serviced?

It was last serviced in December by British gas (if you can call it a service) 

What makes you think it's likely to be the EV? 

How would I rectify fixing an expansion vessel? Costly for an engineer to do it? 

Mr.Generous

I'd say expansion vessel has failed. typical symptom is falling pressure so you top up, then it goes too high when heating used. Ultimately the PRV will activate and usually needs replacing too once this happens.

You could try pumping it up a bit, normally a car / bicycle tyre valve you just top up with a bike pump, but once they start failing normally best to replace.

shiraz99

Mr.Generous said:

I'd say expansion vessel has failed. typical symptom is falling pressure so you top up, then it goes too high when heating used. Ultimately the PRV will activate and usually needs replacing too once this happens.

You could try pumping it up a bit, normally a car / bicycle tyre valve you just top up with a bike pump, but once they start failing normally best to replace.

I wouldn't recommend randomly pumping up the expansion vessel. For a start the boiler should be drained down beforehand and also as you're opening up the boiler case it would be something for a gas safe to do, and whilst it's an easy job it's not really a diy one.

macman

Get an independent GSR RGI in, it's not a major job, especially now you've already got a diagnosis.
BG will probably recommend a new boiler...

jefaz07

30 minute job! Parts aren’t expensive either. Although If it’s been sitting it may just need re inflated.