Main combi 30 Eco DHW gets hot until... the CH is calling

[Backboiler]

Can anyone confirm my thoughts on a solution to this boiler fault? Went to the above boiler yesterday and the hot water works perfectly until there's a demand for CH. The hot water keeps going cold when there's a demand for heating. The hall sensor was lighting on HW demand. I took off the motor head and the pin was moving but it was buzzing. Faulty intermittent motor or cartridge passing? The PCB has been replaced by a previous engineer who walked off the job.

 

[Leo21]

So when the hot waters running when you create a central heating demand, the hot water fails?

 

[Backboiler]

So when the hot waters running when you create a central heating demand, the hot water fails?

Yep. That's correct. And when the CH is running if you turn a HW tap on, the HW water runs cold.

 

[Leo21]

To my mind the diverter should prioritise the hot water. So the actuator shouldn't move. My first thoughts would be pcb, but that's been done.
The only other thing it can be is a small amount of voltage passing, and the actuater being weak.
I'd ring the tech help line up.

 

[Backboiler]

I did notice the Div motor buzzing (humming) so I removed it and noticed the spindle wasn't moving when switching, even when I tried to press the pin with a screwdriver, but after I pressed the pin a few times it moved. I re fitted the motor and all appeared to be working as it should,,,,,,,, but I got the dreaded call the next day to say it was exactly the same again. I've ordered a motor and a cartridge kit and I'm going to fit in that order and see what happens. It's jobs like these where you lose money and it's in our blummin nature not to give up. Thanks for reply Leo