Vaillant combi heating coming on at random...

[Artisan Bathrooms]

Hi Gents,

I'm after a bit of advice about a misbehaving boiler if poss. Customer has a Vaillant turbomax combi about 3-4 years old. Works fine, but heating sometimes comes on at random in the middle of the day or early hours of the morning when it's not supposed to. She's had a new programmer to replace some ancient one hanging off the wall which is working fine but the boiler still misbehaves as before. My rgi is skiving for three weeks in Brasil so we can't get him to check it over.

My questions are basically..
1. Does it sound like the pcb is a bit dodgy,
2. How can I tell, and
3. Is this something I could replace (experienced plumber and reasonable electrics but not corgi).

Cheers in advance..

 

[gas4you]

Could possibly be DV stuck mid position and the HW pre-heat is on, so the rads will get warm when pre-heat fires up.

 

[Artisan Bathrooms]

Cheers for that Dave.

Could the HW pre-heat properly warm the place up through a passing DV? It doesn't just come on for a bit - her flat was apparently at 18 degrees this lunchtime.

Pete