Trianco TSB boiler

keystone

Ok if you think it's the valve:

1. Remove actuator head from valve so that you can observe what it is doing with 2. below.

2. Turn the tankstat right down. Get someone to operate the CH thermostat so that it calls for heat and then turn it down. Does the head operate? Then check it again with CH off using the tank stat. Does it operate now? Try it again with both CH and DHW calling for heat. Does it operate now?

3. Try and operate the valve using an adjustable spanner on the spindle. Does it turn easily or is there resistance.

If the head operates OK its not the head. If the valve itself is gummed up then repeatedly operating it with the spanner may free it up. If the head needs replacing its a simple enough job - jut make sure you get like for like and wire it the same way. If the valve itself needs replacing then you are looking at a partial draindown. Again try and get like for like so that dimensionally it is the same and piping alterations won't be needed.

HTH

Cheers