Central Heating Fault, Diverter Valve?

Bit of an issue with my central heating this past few days, it's struggling to come on.

When I turn up the temperature to trigger the heating, it often seems to fail. It's hard to say how often, because it can work fine for a few minutes whilst testing, but then minutes later, or a day later, fail.

One of the diverter valves is making a strange buzzing and clicking/tapping sound - I'm not sure if it's normal, but I'm guessing not?

When it works, I will hear the click of the thermostat, then a whirring of the valve and then the boiler comes on. When it fails, I hear the click of the thermostat and then nothing at all.

I made a short video clip here, so perhaps someone with more experience can offer some information?


The noise seems to be coming from the bottom unit.


If it's relevant:
Boiler is a Worcester Greenstar 12i system boiler (showing 2 bar / just under)
Thermostat is a 3rd generation Nest
Unvented cylinder as part of the system
Every single component in the entire system is just a few months old.

Firstly, unlikely you have more than one diverter valve, more likely two motorised valves.
You have answered your own question by indicating the thermostat click does not always result in boiler firing.
When timer switches on, thermostat associated with that zone, if calling for heat, will power the motorised valve. Valve opens and boiler runs

Such a setup needs a bypass and I strongly suspect pump under control of boiler. Have seen instals done by supposed pros even, without these causing all sorts of problems

Skiny said:

One of the diverter valves is making a strange buzzing and clicking/tapping sound

Click to expand...

Which zone does the above diverter valve serve ? If its on the central heating zone it sounds like the culprit.As long as the system is installed correctly and any alterations have been carried out correctly.

That youtube vid is not working unless you were filming snow at midnight,

Post some pics of the zone valve arrangement,pipe arrangement.

The video should work. Here's the direct link if not:

As far as I know, yes, it controls the heating. When I can get the heating to come on (often after a few on/off attempts with the thermostat), that bottom valve makes a noise, as shown in the video.

Anyone?