Non uniform pressure loss in Greenstar 30i

[MrM83]

Dear All,

I hope you might be able to point me in the right direction with an issue I have with a 3 year old Greenstar 30i boiler, last serviced in Oct ‘22, with new pipe work all around the house at time of boiler install. We have separate circuits upstairs and down and a water cylinder.

At the service I mentioned to the engineer that it does seem to slowly lose pressure. The prior year I probably topped it up 2 or 3 times.

Since it has been serviced and over the cold snap the pressure drop has become more regular, but the behaviour is strange and I wondered if I could ask for an expert opinion.

When cold I have pressurised the boiler to ~1.4 bar, approximately middle of the green range on the pressure dial. This dial can rise to just under 3 bar, the top of the green range on the valve at times. Over time (days/weeks) the resting pressure seems to drop to just above 1 bar, then all of a sudden one day it will drop to a smidge more than 0. So gradual drop, followed by an abrupt one. This process took about 4 days to happen during the cold snap, then has just happened again after about 10 days.

The range in pressure from the boiler being off to on seems to be 1.5 bar at most. Having fallen to almost no pressure and off, the boiler will then rise to ~1.5 bar when it fires up and gets going.

I have bled all my radiators and found no air in any of them. The engineer who serviced the boiler mentioned the chance of a microscopic leak either in the pipe work or in the boiler. What is baffling me is what would cause the gradual decrease and then a sudden slump in pressure. I would have thought if I had a leak then it would fall to zero after a period of being at the upper pressure range?

I’m not sure if relevant but radiator water temperature is currently set to 68c and when the boiler fires up from cold there is a bubbling noise from within the boiler.

I had booked the company who did the service to come and take a look before Christmas but they cancelled on me on the day due and having taken a days holiday in anticipation of them coming, I was irked enough not to rebook a visit at that point in time.

Can anyone enlighten me as to what the problem might be here? Thanks very much!

 

[ShaunCorbs]

Sounds like your heating pressure valve might of actuated with the system pressure being close to 3 bar shouldn’t be that high so sounds like your expansion vessel is too small I’m guessing you have over 10 rads ?

 

[MrM83]

Thanks for your reply. We do over over 10 radiators. After my initial post I thought I should check the external pipe given the larger pressure drop would have been recent and sure enough there was evidence of water escape.

I am suspecting some issue with the expansion vessel/ pressure valve. The engineer that did the recent service suggested pressure should be between 1 and 1.5 bar when cold, obviously I have no control over the pressure when the boiler is firing. The expansion vessel is internal.

I’m still slightly confused as to why the pressure valve would only actuate after a period of days/weeks has elapsed post opening the flow valve to re-pressurise to 1-1.5 bar? I would have thought this would happen immediately when the boiler gets going?

I know nothing about how a pressure valve works, nor how they fail. Are they easy to replace and would this likely solve my issue?

Thanks again for taking the time to reply.

 

[ShaunCorbs]

Need to have an external expansion vessel fitted as you shouldn’t have over a bar expansion eg 1.2 cold 2.2 max fully hot pressure

Also the prv needs replacing as they don’t seal fully when used

 

[MrM83]

Thanks very much for your help.