I have problems with my vented c/h system making banging noises in the boiler and pumping over into the f/e tank.
The system is about 12 years old with TRVs on all but 2 rads. The Myson Orion Fanfare boiler was moved and extra rads added just over a year ago.
About 20 mins or so after it first comes on in the morning there is a rumbling/banging/rattling noise in the boiler for a few seconds and the system pumps over. Often it is then fine for the rest of the day, but sometimes it will repeat it later on. Occassionally it has done it repeatedly for 5-10 mins! At the point the rumbling/banging starts the sound of the water going round the rads dies down for a second and then surges (causing the pumping over) before going back to its normal speed.
I initially thought it was the pump as it was noisy and did jam once so I changed that, however it has not solved the problem. It's 3 speed and is currently set on 2. I tried turning it down to 1 (as is often suggested to stop pumping over) but this made it worse. Unfortunately, running it on speed 2 makes the water circulating round the rads quite noisy!
I also had problems the other day with the f/e tank overflowing and pulling in fresh water at the same time so I've temporarily got the cold feed to the tank turned off. What level of water should there be in the tank? Mine was about 2/3 full with the end of the overflow dipping down below the surface, although there was no leak from the cold feed. With the cold feed off and rads bled, the level is remaining at just below halfway but I obviously need to set a level and get the supply turned back on.
I realise the pumping over is not good for the system and needs fixing as it will be causing corrosion, so what are the likely causes? Searching various forums etc. suggestions seem to be:
- faulty pump? - well it's been replaced and I've checked the electrics to make sure its not cutting out
- pump too fast? - it's worse when turned down
- bad design? - it used to be ok!
- f/e tank level too high? - it's still happening with the level reduced and again it used to be ok!
- a blockage? - possible, but all rads get hot (very hot!) so I think this is unlikely
- faulty boiler thermostat? - I currently think this may be the most likely cause (especially with the very hot rads?) Is there a simple check/test I can do to confirm this before calling out a Corgi to fix it, bearing in mind the fault is intermittent?
Thanks in advance for any help/advice……..