Boiler water pressure problems

[anonymous-user]

So Worcester Bosch Greenstart 24i junior

The water pressure dial is sometimes right up into the red, other times right down at zero and needing topping up to work

It runs a shower and three radiators that's all

My guess is that there is a leak somewhere and when the heating comes on via the thermostat, water is being lost from the system somewhere

Am I right? Or is it possibly something else

[shtu]

Sounds like the expansion vessel has failed or needs recharging.

[silversurfer1]

Probably right yes, the expansion vestal takes up the increase in volume of the water when its heated, the the vestal has lost its charge the air space will be missing so the water has nowhere to expand into.

With nowhere to go the pressure will build whilst the heating is on and then at 3bar the pressure relief valve will lift to allow water out and the pressure to fall back to less than 3 bar.

No the heating turns off and you have lost volume through the prv when the system cools your gauge now shows 0.

isolate and drain boiler leaving drain off open , get a pump and attach to the vestal and charge to about 0.7 bar or different if it states on the vestal.

Re fill system if your prv is not knackerd your all good to go

ss

[Hoink]

I'm no expert but had similar issues with my boiler - as mentioned above it turned out to be the expansion vessel and prv. Both were replaced.

Edited by Hoink on Monday 22 December 17:22

[andySC]

It's almost certainly a expansion vessel issue, either there is no charge in it (easy fix) or it has failed (not so easy). The other issue is the pressure relief valve. On the Greenstar range it's in a very awkward place & if it's had it I'd recommend finding an engineer who is familiar with this type of boiler or have WB themselves have a look at it. They do a fixed price service for repairs & if the vessel & PRV have failed this would be the best option in my view.

[no effort]

Sounds very similar to our boiler problem which we had fixed today. The plumber connected an external expansion vessel.
We decided to go for the cheap fix as we'll probably replace the boiler in a couple of years.

[anonymous-user]

thanks all, will look into the expansion vessel situaiton first and, if I can't work out how to fix it, get on to WB

have found a few threads on plumbing forums about what to do and will see how it pans out tomorrow...

Edited by anonymous-user on Monday 22 December 21:24