My hot water is working fine, boiler fires up OK.

The problem is that my heating won't switch on.

I have a wireless thermostat which appears to send and receive the correct signal as the receiver switches on and off when I change temp of the sender and I get all the right lights.

Every now and then I can get it to come on but I have to turn temp up and down until it switches in - sometimes I have to do this for an hour or more.

I have an Ideal/Icos boiler (not combi) about 8 years old.

Any suggestions please.

  • Does the wireless receiver have an override switch? If so does that work 100% when you use it? Does the wireless thermostat work better when you move it near the receiver? Note: even if the thermostat is calling for heat some boilers wont turn on until the temperature drops (to prevent rapid on-off cycling) Mar 1, 2016 at 10:36
  • Could a low battery be causing intermittent signal transmission?
    – Ed Beal
    Mar 1, 2016 at 14:17
  • 1
    If transmission is working well, could the connection between the receiver and boiler have become damaged? Could a circulating pump or zone controller have failed? Mar 1, 2016 at 15:08
  • Thermostat appears to be functioning correctly Room Temp 16, Thermostat 30 and it switches in on the remote side. Connection could be faulty but don't see how as it is nowhere near anywhere that people would need to touch it. I'm thinking 3 way motorised valve.
    – Dave
    Mar 1, 2016 at 16:09
  • The valve moves to the auto position when hot water comes on. When water goes off the slider becomes loose. I can force it to the manual position but nothing happens and the switch becomes loose again.
    – Dave
    Mar 1, 2016 at 16:11

1 Answer 1


I had this recently with a recently installed Tado thermostat and 8-year old Horstmann diverter valve.

The valve was found to be sticking, The thermostat was fine.

Yo can check this by unscrewing and lifting the diverter head off the valve, the turning the valve to the hot water position with pliers.

In my case, the radiators started to warm immediately. Putting the head back on the valve reinstated the hot water only situation. Moving the manual override lever on the valve head had no effect.

A new diverter valve fixed the problem.

  • Think I'll try this before I do anything else. Should at least tell me what the problem is,
    – Dave
    Mar 1, 2016 at 22:51
  • 2
    Looks like I had a loose wire in the connection box, heating issue resolved itself when I moved the box. Not going to touch it unless the problem resurfaces as the house is starting to warm up.
    – Dave
    Mar 2, 2016 at 10:36
  • 1
    @Dave -- post that as an answer and I'll upvote Jun 30, 2016 at 0:20

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