Thanks, ***** ***** a play around. The flame rectification sensor is worth checking out and I have been lead up the garden path before now by the air pressure switch. Having said that, I have noticed in the past hour that opening the hot tap at full whack produces hot water no prob which could suggest the pressure switch is not sending the right signal when the tap is opened nomally or slowly.
Hi, Sorry I had to have a little knap. It's now lookin more like a diverter valve problem as I have raised the central heating thermostat and switched to both ch and hw on demand. The wireles is calling for the heating but no response over an hour or so.
Will wait till Monday to see what Vaillant have to say and when we reach a positive outcome I will rate your answer. So far so good. I appreciate how difficult it is in this particular instance to pin it down. I have had about 4 diverter valves over the lifetime of this boiler and I'm surpised that technology has not come up with something more robust and reliable. Just saw your message. The HW came on smoothly