Green star Combi boiler overheat problem

hockey2019

Have set CH to 4 and HW 3 - pressure rises by 1.5bar stays just under the red lines - will check the EV tomorrow when the boiler is cold 

glennevis

FreeBear said:

ThisIsWeird said: Provided you can gain access to it without opening a panel that affects the combustion area, then it can usually be checked quite easily.

The EV will be internal to the boiler on a Greenstar. So to gain access will require breaking the seal of the combustion area. Gas Safe engineer territory I'm afraid.

On all the Greenstar boiler I've had the EV is at the back of the boiler at the top, so it is visible from above (big red oxide coloured circular vessel). The Schrader valve is at the top and should be accessible without removing the case. So after you remove the plastic cap on the valve (just like on a vehicle) you can check and repressurise the EV without a GS engineer then follow the procedure @ThisIsWeirddescribes.

FreeBear

glennevis said:

FreeBear said:

ThisIsWeird said: Provided you can gain access to it without opening a panel that affects the combustion area, then it can usually be checked quite easily.

The EV will be internal to the boiler on a Greenstar. So to gain access will require breaking the seal of the combustion area. Gas Safe engineer territory I'm afraid.

On all the Greenstar boiler I've had the EV is at the back of the boiler at the top, so it is visible from above (big red oxide coloured circular vessel). The Schrader valve is at the top and should be accessible without removing the case. So after you remove the plastic cap on the valve (just like on a vehicle) you can check and repressurise the EV without a GS engineer then follow the procedure @ThisIsWeirddescribes.

I stand corrected..

BUT... Designs change, and the Greenstar has gone through may revisions since it was first launched. The EV might not be accessible depending on age & exact model.

hockey2019

Quick update - had to drain system to release all the pressure - then checked EV no pressure at all - pulped up to .9 bar as stated on sticker on side - now system is balance on pressure all good no more overheating thanks everyone for the advice 

Mr.Generous

I'd start getting prices to replace the expansion vessel, once they lose pressure they usually do so again and again.

hockey2019

Thanks for the info - will keep an eye the pressure and see if it changes 

ThisIsWeird

The test for a kaput EV is to press the valve pin whilst the system has some pressure - that way any water present on the air side should spurt out. Since you depressurised the system side, and because there was also no pressure left in the air side, any water wouldn't be ejected even if present.
But, let's hope and assume that the EV is actually fine, and the air loos was not unusual, and took place over years. Good chance it's fine, and the air seeped out via the valve cap, very slowly.
Just keep an eye on it, especially any rising of pressure. If the diaphragm is leaking air, you'll likely find it in your radiators! 
Anyhoo, fingers crossed - and well done