Despite x400 not making a difference, could cause be sludge/deposit partially blocking near the cold feed connection or near the start of the vent pipe (or somewhere else in the system)? Would a re-dosing with x400 then flush be appropriate?
Also I have noticed that the cylinder thermo is...
Well I've produced a diagram using Word but I can't download it into the post. As far as I can see the flow is:
Boiler => Pump => Hot Water Cylinder => Return pipe =>Boiler
....................... => Valve => Radiators => Return pipe => Boiler
After the pump there's a 3-way junction...
I'll try
But while I'm trying to draw the diagram is there anything which might be obvious to you or other experts possibly causing the overflow? and which I as the poor householder would miss.
Meanwhile thanks for your responses so far
Overflow lasts about 15 seconds
Again - definitely 2-port
Ahhh - I'm confused (I'm no expert) but it seems that the return is on the output side of pump.
Definitely 2-port.
I'm only speculating about operation of boiler thermostat since I don't see how the system shuts down when both room and cylinder thermos satisfied. It may be that system does shut down correctly. But for the last 25 years the system has worked satisfactorily.
Sorry – been a bit dim – not useful info in my last posting
Flow is boiler => pump => return => valve =>
Valve is 2-zone valve. system default is flow to hot water cylinder. Heating circuit opens when thermostat operates ie hot water always on except when cylinder thermostat closes and...
Boiler, pump, motorised valve all in a small outhouse backing on to fireplace at side of house ie the boiler flue uses the old chimney flue. F&E tank at top of house (3 stories up).
Umbongo
System: fully pumped/open vented/14 rads/3 stories
Boiler: Gas: Potterton Kingfisher MF CFL 100
New boiler (as above) installed about 5 months ago into 25 year-old small-bore system which was flushed – but not power-flushed – at new installation. System well maintained containing inhibitor...