My Worcester 19/24CBi boiler keeps overflowing into the header tank via the expansion pipe. Whilst reducing the water in the header tank I found the expansion pipe discharging hot water (a total of 5.4 litres whilst I was collecting it).
The central heating is OFF and the pump isn't running.
I've tried lowering the temperature settings at the boiler and the hot water cylinder but it makes no difference (apart from a cool shower).
Any advice please?
John Howard (Kent)

John Howard, July 2010

If you put the pump on speed 1 (lowest), and there is no pumping over and everything works ok, leave it there.

Carefree, July 2010

Dear Carefree
Thanks for your speedy response - I had no idea about the pump speed being variable, it was as installed! I've set it down to one (1) so see what happens. I was under the impression that the pump only operated when the controller was in the C/H position "timed"; should I reset the pump to two next time I turn on the C/H?
Much appreciated
John

John Howard, July 2010

You say the pump is OFF?
This situtation is specifically known as 'pumping over' so I suggest when this is occuring, the pump is running. No pump, no water movement.
Could be down to a faulty boiler thermostat (however this is unlikely if you are getting a cooler shower), but don't write it out as a possibilty.

More commonly, the pump setting is too high for the system or wrongly positioned due to poor design of system installation, (ie: Open vent and cold feed not 'close coupled').
Is the water in the F&E cistern red/brown in colour?
It would suggest this has been occuring for some time.

For a temporary solution, try turning the pump speed down to see if it cures the problem, the longer term solution would involve altering the system design, could be as simple as close coupling open vent and cold feed or raising the F&E cistern to a higher position.

Carefree, July 2010