Heating/hot water system at 3.5bar...
Discussion
Just after any advice. I noted yesterday that water was dripping from an open pipe outside (I assumed it was a condensate pipe but thought its strange as the boiler was not running). This morning I checked the boiler (Grant Euroflame 90/120 oil) and the system pressure showed 3.5bar. Now I believe the dripping water was from the pressure relief valve which is supposed to operate at >2.5bar.
My guess is there's a problem with an expansion tank but there are two; one one the boiler and one above the sealed hot water tank.
I did relieve the pressure to 1.5bar by bleeding down a radiator but it crept up again and then the boiler fired up when there was hot water demand. Aside from getting my plumber in is there anything I should do immediately?
My guess is there's a problem with an expansion tank but there are two; one one the boiler and one above the sealed hot water tank.
I did relieve the pressure to 1.5bar by bleeding down a radiator but it crept up again and then the boiler fired up when there was hot water demand. Aside from getting my plumber in is there anything I should do immediately?
Go round all the expansion tanks and rap them with a knuckle. If they sound hollow, good. If they sound solid then you can try adding air with a bicycle pump in the top cave, but the internal rubber diaphragm has probably failed and you’ll need to replace the unit. Which is easy if the installer put a shutoff valve immediately before it (as they should) and usually involves a drain down if they haven’t (as is common).
Thanks for your input. I have just spoken to my local guy and he's going to come round some time today and advised I turn off the system for now. His main concern was that when I told him that I had relieved the pressure but then it had gone back up he said there are only two ways that can happen - the fill valve is not shutting off properly or...the hot water coil has failed 
LastPoster said:
OT slightly but should you really fit an isolation valve just before the vessel, doesn’t this allow the expansion to be shut off (inadvertently maybe)?
Unscrewing the handle should provide sufficient mitigation. For extra protection the handle can also be hidden, never to be found again of course even when legitimately required. Just thought I'd give an update. After my plumber advising the potential causes I monitored the system pressure for 4 hrs with the cold feed to the hot water tank isolated. I had reset the system pressure to ~2bar but even with the boiler not operating the system pressure increased by about 0.2bar per hour. I then opened the cold feed to the hot water tank but this made no difference to the rate of increase.
I then isolated the cold feed to the boiler after resetting the system pressure to 1.5bar (this time the easy way by using the pressure relief valve!). After 2hrs no change so the problem seems to be the fill valve has failed partially open. Plumber booked to fix early next week.
I then isolated the cold feed to the boiler after resetting the system pressure to 1.5bar (this time the easy way by using the pressure relief valve!). After 2hrs no change so the problem seems to be the fill valve has failed partially open. Plumber booked to fix early next week.
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