Combi boiler intrmittent problem

[Peter Brown]

I have bought a house fitted with a Vaillant combi boiler. The unit has been extensively serviced by a vaillant engineer who fitted many new parts. I recently replaced the top up tap which meant draining the system. Since restarting the system the CH seems to work only intermittently. The hot water is fine. The CH when it comes on, starts the process, pumping, clicking, etc, but only fires up sometimes after a little while. This is with timer or manual. It would seem that there is air in the system. The vent on top is open. The rads have all been bled. Is there some thing else I can do? Thanks Peter Brown

[Ed Sirett]

Which model? Try turning the heating thermostat up?

[Graham Tavener]

Have you bled air from the pump? There is an air bleed screw on my Vaillant that should be loose so that trapped air can escape from the pump.

Graham

[Ed Sirett]

Further thought: it sounds much more like an ignition problem than a water one.