No water flowing in Combi CH system - Britony Combi SE

[jm9431]

My boiler fires and heats to 80 degrees C for a short time, then cools back down again quickly. The pipes near the boiler heat up, but only as far as the first radiator downstairs and this rad doesn't get hot. Other downstairs rads are cold. Upstairs rads are reasonably warm, but not as hot as they should be.

Looks to me as the water is not going round the circuit as the downstairs return pipe is cold and upstairs return pipe is only a little warmer. This seems to leave 2 options:

a. Pump is broken
b. There is an airlock

Option a
Pump is vibrating and having removed the centre screw on the Grundfos pump the impellor is going around. Therefore appears to be working, but could be slow or have a damaged impellor?

Option b
Is this possible? I had a similar problem recently and when I bled the radiators upstairs the system worked fine.

I assume the upstairs rads are warming through convection only.

I have considered replacing the pump and draining the system right down and refilling it. Does one of these ideas seem sensible? Should I try anything else? Would either idea cause me any major problems? (I am competent DIYer and electrical engineer)

 

[Agile]

Before you do anything drastic why dont you just clean the gauze filter on the return at the entry to the boiler?

Thats assuming its been fitted in the right place and that you can find it hidden away somewhere inside the valve assembly.

If that does not fix it then disconnect the DHW flow switch plug and see if the diverter valve then reverts to the CH position.

If that really does not get it working then you have got to do some very clever manipulation to get the diverter valve apart. Its simple when you know how but impossible to describe in words!


Tony Glazier

 

[Gasguru]

As the hot water performance is OK the pump is probably working fine.

I can't remember whether there is a filter (may be blocked) on the return pipework connection to this boiler.

A common problem with this boiler is a sticking diverter valve - jams up and the motor head can't move it.

From memory its a straighforward job (although the boiler pipework needs a lot of force to change the valve)

Change the auto air vent at the same time (non standard and often leak)