Honeywell heating controls broken

[dvans]

Hi,

I have a system with Honeywell heating controls and a Sunvic thermostat. Not sure what model the controls are but look like an older version of the ST699.

The thermostat had been wired in reverse so decided to fix it today. The wiring diagram I found suggested swapping 1 and 2 wires on the Sunvic would fix it but this was wrong and when I switched the system back on it blew the spur fuse as well as tripping the main RCD.

Checked the thermostat with a meter and it should have been 1 and 3 wires which were switched. I've done this and replaced the spur fuse and now the thermostat works properly but the heating controls do nothing.

The controls display works fine and on/off LEDs work as expected with the switch but there's no effect at the boiler, CH stays permanently on. Boiler goes off and on depending on the thermostat and with the thermostat off, HW controls don't do anything either.

Is this likely the control unit or something at the boiler end?

Thanks,

Neil

 

[Dan Robinson]

You've probably fused the relays in the clock.

You can still get them, but they're not the cheapest.

 

[45yearsagasman]

Either what Dan suggested, or a zone/motorised valve is cream crackered and keeping the boiler on.

 

[Dan Robinson]

Possibly. But hopefully the boiler is okay could be an expensive mistake.

 

[dvans]

Thanks guys. I've pulled the panel off and at the very least there's a blown resistor. It's definitely a ST699 and the local Screwfix have them in stock so I think I'll just pop down and get a new one before the missus gets home.

 

[dvans]

New control unit in place and all working properly now.

Thanks again for the advice.