Issue with Honeywell thermostat no heat control only on/off

Discussion in 'Engineers' Talk' started by turbo2015, Dec 1, 2018.

  1. turbo2015

    turbo2015 Member

    Hi all...any help will be most appreciated

    my Honeywell thermostat only seems to work as a on/off switch and does not control the heat of the rads.... it either turns the heater on at full force or shuts them down. (essentially just a on/off switch)

    There is no heat control on the boiler end either.

    The boiler end also has a timer which seem to work fine.

    Ive replaced the thermostat and still no luck. is it wired right? what should i do, driving me mad, hard work to keep the house at a comfortable temperature.

    Thanks All

  2. Allsorts

    Allsorts Well-Known Member

    Hi Turbo.

    I'm afraid that's all a wall thermostat does - switch yer boiler off when the room temp reaches that set on the dial, and then turns it back on when it falls below this - 'click'.

    Having said that, your stat does have a wire missing - a Neutral. Adding this would make it more sensitive and react more closely to the set temp.

    Is the issue you are having that the temp setting is 'crude'? Ie say you set it to 20oC the boiler will come on and the rads heat up but it can get a bit warmer than this before the stat goes 'click' and turns off the boiler. And then the room temps drops by a noticeable - uncomfortable amount - before it clicks on again?

    When you turn the stat control up and down past the 'click' position, is the click happening at what the actual room temp is? Or close to?

    IF the issue is that it does 'work' but it's 'sluggish' - ie allows too great a temp swing above and below the set temp - then adding a new wire - a Neutral - should help, and this would go to '2'. (NB - that BLUE wire you currently have is NOT a 'Neutral' - it's almost certainly the 'switched live'...). But if running a new wire is awkward, then a better solution would be to buy a battery-operated digital 'stat (better still a 'programmable' type) which will only need these two wires but will be more accurate.

    First thing - does it 'work' to some extent? Does it turn the boiler on and off as you turn it up and down? If so, how close to the actual room temp does it go 'click'?

    Second thing - what's that white screw terminal doing at the top of your stat - are any wires going to this? What's it for?
  3. turbo2015

    turbo2015 Member

    Hi Mate

    Thanks for the detailed reply....

    The current Honywell installed is T6360....when turning the dial its click on at just above 10 degrees mark, the room could be at 30 degress but will always click's on when turning the dialing just above 10 degress.

    Just seems to work like a on-off switch no matter what the room temp. This leads to problems as the boiler overheats the house, and is running at full chant even if i only need to rads to be at a mild temp to keep the house warm.

    I have replaced the Honeywell for another one of the same make and the new one does exactly the same.

    What i would like is to control the temp of the heaters from the Honeywell, The honeywell is located downstairs, the upstairs heats up alot faster then the downstairs, during the night can get very hot, having a thermostat downstairs's may not help even if it was working. Can i do anything (rewire) to set it as a heat control for all rads?

    Ive attached a clearer picture with cabling diagram

    Cheers Again


  4. Isitreally

    Isitreally Well-Known Member

    Sort this wire out causes you trouble.


    It looks to be a two wire stat so no neutral needed, the blue in this case is the call feed back to the port valve and should be marked with some coloured tape to mark it as so ( my I've used yellow tape.)
    Allsorts likes this.
  5. Allsorts

    Allsorts Well-Known Member

    Hi Turbs.

    Your stat would appear to be wired 'correctly' although - in lacking a Neutral - it's compromised in its performance in that it'll be more 'sluggish' to respond to room temp fluctuations.

    First things first... You say that this stat 'clicks' at around 10oC even if the room it's in is at 20-odd? That means one thing only - the stat is knackered. You say you've swapped the stat and the new one does exactly the same? That means only one thing - the new stat is knackered.

    OR, you are mistaken.

    If you take an analogue (electro-mechanical) stat like yours out of a box and don't even wire it up, it will still 'click' at the room temp.

    What does adding a Neutral do? If you look at the wiring diag - Standard with Anticipator - you will see a zig-zaggy thing being connected at the same time as 1 joins with 3. This heats up the wee z-zag which makes the crude stat react more quickly. The idea is that it switches on and off more quickly around the temp it's been set at.

    Yours doesn't have this Neutral so the zig-zag doesn't work. BUT it should still click at close to the actual room temp.

    I don't understand why 2 of your stats don't do this.

    The single best solution would be to fit a battery-operated stat - that only needs 2 wires.
  6. dobbie

    dobbie Well-Known Member

    It is a 3 wire stat, no 2 is for the neutral therefore it will not work as well as it should without the neutral.
  7. Allsorts

    Allsorts Well-Known Member

    Getting the up and down stairs to a good balance is a different matter. The ideal solution is to 'zone' them so they work independently of eachother and each has its own wall stat, but that's a fair bit of work - adding a valve to the flow pipe, fitting a room stat upstairs, running a cable back to the boiler...

    It might be a simple case of balancing the system so the rads heat up at the right speed - the upstairs ones more slowly since it'll also be getting heat from below. This is done by adjusting the lockshield valves - have a surf for 'balancing a CH system' or similar.

    Or, why don;t you just turn down the rad's TRVs?!

Share This Page