Problems after swapping T6360B for TP5000si thermostat

[Kieran42]

Hello,

Apologies first if this has already been asked but I couldn't find the answer or help I was looking for.

I have a conventional boiler and I recently swapped out my mechanical Honeywell T6360B room thermostat
for the digital battery powered Danfoss TP5000si. After completing the set (as per the user guide), I tested
the tp5000si by raising the desired temperature above the displayed room temperature and as expected the
central heating came on. However when I lowered the desired temperature to below the room temperature
the central heating rather than turning off remained on!  I even went to the separate CH & HW
programmer and switched the CH off from there but the boiler kept on running and wouldn't switch off!...
So the question I have is have I wired it wrong or is the tp5000si faulty?
  
The original wiring set up for the Honeywell T6360B was as follows:

    T1  -- Live-IN                         (Brown cable)
    T2  -- Neutral                        (Blue cable)
    T3  -- Switched Live-OUT    (Yellow/Green Cable)

For the TP5000si the new wiring set up is as follows:

    1(OFF)    --                             (No cable Connected)
    2(COM)  --  Live-IN               (Brown Cable)
    3(ON)     --  Switched Live   (Yellow/Green Cable)

    (The Neutral blue cable is left disconnected via an insulated terminal block)

As far as I am aware the wiring all looks fine... so I am puzzled why the central heating keeps coming
on and off on it's own accord even when the disired temperature is set below the room temperature???

Your thoughts on this would be much appreciated.

Thanks

PS: Wanted to upload some photos but couldn't work out how?

 

[ProDave]

If it won't turn off from the programmer either, I would look at a different fault, perhaps a stuck motorised valve that just happens to have gone wrong at the same time.

As a sanity check, put the old thermostat back and see if the fault goes away or not.

P.S whoever was there before you wired it with the wrong cable. You should NOT be using green / yellow as switched live.

If you can get the new themostat working and can find the other end of the cable, then as you only need 2 cores, use the blue (with brown sleeving on it) for the switched live.

 

[Kieran42]

Thanks ProDave,

Just so you know the boiler is a Glowworm Micron 60FF, and the boiler, programmer & t6360B mechanical thermostat were all fitted about 15years ago by a Corgi Registered heating engineer. I still have the Installation Log Book with the chaps Corgi Registration details.... but he's retired now.

Someone else mentioned that it's of concern that the programmer isn't able to switch off the boiler... but I did use a Corgi registered heating engineer so you'd  think it should have all been wired correctly... but one never knows!

I've put the old thermostat back and it's all working fine again, programmer is also able to control the CH, so it can't be a stuck motorised valve then can it?

I would like to get the digital tp5000si working as I find the old mechanical one inaccurate by at least 2-3 degrees.

So just to clarify your last suggestion...  should I leave the Brown (live-IN) cable connected to "2(COM)" and instead of the Yellow/Green cable connect the Blue cable to "3(ON)" as the Switched Live?

 

[ProDave]

CORGI (now Gas Safe) means he has done the courses and assessments and is safe to do gas plumbing. It does NOT mean he knows anything about electrics or how to correctly wire a heating system.

Yes use the blue cable BUT you MUST find the other end and make the same change there as well.