URGENT Help needed please - Blown heating fuse...

[John Rumm]

The real problem is that the old stat has a connection that is simply not present on the new ones - i.e. the neutral for its internal heater. Other than that they are about the same.

[John Rumm]

Both ought to be checked. The valve will probably have a switch that is actuated by the mechanism when it reaches the end of its travel.

[Rob Morley]

It's the box with a clock where you set the times you want the water and heating to switch on and off.

[Dave Liquorice]

It might have been useful to add a note about your yellow/green problem. It would have avoided some of the confusion and concern.

Oh dear. But I guess if you are paying the sub you may as well try and get your monies worth.

Something else has failed in an attempt to protect the fuse, which shouldn't have been a 13A one in the first place. 3A is more than adequate.

Depending on how your system is wired the blown bit could be in the boiler, the programmer or wiring center. The fault current isn't likely to have travelled through the valve electrics.

Normally the incoming mains comes from the switch fuse unit to the programmer, to the room stat, to the valve motor. With the wiring center possibly being between each of those items. As you put a live/neutral short on at the room stat I suspect the programmer has a burn out track or exploded relay; or the wiring center has a vapourised track. I see elsewhere you say the programmer is a rotary type, these are generally pretty bomb proof but may still have a bit of PCB track taking the power to/from the contacts.

Of course you do you've opened the valve.

[Richard Marx]

Hi all, it's sorted. It wasn't the wiring or the stat, it was the heating controller (wall timer) which had gone, all thanks to the previous occupants putting a 13A fuse in the system.

British Gas came to my rescue, fitted a lovely new light-up-in-the-dark digital programmable controller, and all is now working perfectly inc. the new stat I fitted yesterday. Not bad as I've only paid them £16 since I moved in!

Muchos kudos to all those of you who were kind enough to offer constructive suggestions, or who guessed correctly what the cause was.

[John Rumm]

Glad it is fixed!

Yup - not as trivial as many people seem to think. A 13A fuse will let through *way* more than 13A before blowing and that can do quite some damage.