Hot water only when radiators on - Vaillant 428

[sbis]

Hi all, we’ve just moved house and have a conventional boiler (Vaillant ecoTEC Plus 428) with a hot water tank. Always had combi boilers before.

When the heating is on, the water gets hot, but not vice versa. When selecting hot water only via Hive, the boiler doesn’t fire even when the hot water is cold.

I can hear the hot water tank thermostat click when adjusted. It’s set to 55c. The boiler has separate controls for hot water and the radiators, both are set to 60c.

There’s a Honeywell motorised valve to the cylinder which I can operate manually - I’ve heard it close. There’s also a Drayton Zone valve actuator on the flow (no idea what it does) and I’ve seen this move.

I’m happy to pay to get it fixed, but local engineers can’t fit us in until after Christmas.

Would really appreciate suggestions as to what’s going on. Thanks, Steve

Here’s the airing cupboard…there’s lots going on

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[ericmark]

Hive will if set up correct operate the motorised valve, then micro switches in the valve work boiler and pump, it seems likely the micro switch has failed in the motorised valve.

[sbis]

Thanks. Assume I just the whole powerhead on the valve as opposed to just a micro switch?

When turning on the central heating only, the valve circled red moves - but doesn’t do anything when I turn on the hot water.

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Is it the valve that sends the signal to the pump and the boiler? I assumed the thermostat on the cylinder would demand hot water from the boiler.

Thanks again.

[sbis]

Reporting back, you were absolutely right and the micro switch had failed. Replaced with a new powerhead and all sorted.

Very grateful. Happy Christmas all.