Ask The Trades - Print Page

Ask The Trades
https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Baxi 105E boiling then going off https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1492256156 Message started by Martin475 on Apr 15^th, 2017, 12:35pm

Title: Baxi 105E boiling then going off
Post by Martin475 on Apr 15^th, 2017, 12:35pm

Can anybody help. My boiler recently stopped working. I have replaced the diverter and hot water diaphragms because I had them anyway. I have also replaced the Thermistors as one of them had degraded. So after doing this I expected it to work. Unfortunately it fires up when switched on and then makes awful boiling / banging noises. The heat indicators rapidly rise to 80 then it switches off. The obvious thing is the pump, so I removed the pump wired it up (I am an electrical engineer) and it works fine. I then thought maybe the circuit board is not switching the pump on (although I could hear it, but you never know) so I powered the pump individually to ensure it was running constantly. I have drained the system and refilled so there cant be a total blockage as far as I can see. ANY IDEAS?

Title: Re: Baxi 105E boiling then going off
Post by Headrush on Apr 15^th, 2017, 3:14pm

It does sound very much like a circulation problem as you already suspected. Maybe the pump runs but is just weak. I've replaced many pumps in various systems that appeared to work fine but didn't have the strength to circulate round the rads.

Another thought (however unlikely), has one of the flow or return valves at the boiler been inadvertantly closed off. Maybe they have even broke. Again I've seen valves that seem to rotate on the outside but nothing is happening on the inside.

Does the flow pipe from the boiler heat up quickly? How far along the pipe does it heat up? If the answer is yes but not very far then you either have a weak pump or a restriction in the circulation. If the pipe heats up gently from cold, that's because it's drawing plenty of cold water from the return, assuming all else is well with the boiler.

When you run the DHW, can you see the diverter valve moving freely? Does it back off fully when you close the tap? I'm clutching at straws here but there could be all manner of things causing a circulation problem..

Title: Re: Baxi 105E boiling then going off
Post by thescruff on Apr 18^th, 2017, 4:51pm

Are we talking hot water only mode or heating only mode, a blockage would be the best guess at the moment.

Did you check the ports on the pump and the valves for sludge.