Honeywell DT90E thermostat issue

[mikeke]

I have just replaced an old honeywell thermostat with a new DT90E after reading several threads on this site seemed to be a good bet.

i wired it up using red to A and yellow to B and isolated blue and earth as i read they do not need to be used.

the thermostat is working great with good control of temp except that the central heating system does not go on in the morning at the preset time ie 0520. the heating timer is set to go on at 0520 and off at 2230, the heating goes off at night and does not come on as programmed. the only way at the moment i can get the heating to come on is to turn off the thermostat and then turn on again and the boiler fires up no problem and runs as required during the day to maintain the set temperature.

the dt90e is set to factory defaults and is running on a 3amp circuit if that helps,

if anyone could advise how i can resolve this or if i need to change any settings in installer mode to get the heating to come on as set in the morning that would be great.

thanks mikeke

 

[bengasman]

The colour of the wires means absolutely nothing here. You will have to trace the wires or measure to see what leads to what, and then compare with the manuals.

 

[D_Hailsham]

The colour of the wires means absolutely nothing here. You will have to trace the wires or measure to see what leads to what, and then compare with the manuals.

But if it was wired incorrectly the boiler would never light.

To OP

1. What is the set temperature first thing in the morning?
2. What is the actual temperature first thing in the morning?
3. Is the flame symbol showing first thing in the morning?
4. Do you have a well insulated house?
5. Have you changed the batteries?

 

[mikeke]

The colour of the wires means absolutely nothing here. You will have to trace the wires or measure to see what leads to what, and then compare with the manuals.

But if it was wired incorrectly the boiler would never light.

To OP

1. What is the set temperature first thing in the morning?
2. What is the actual temperature first thing in the morning?
3. Is the flame symbol showing first thing in the morning?
4. Do you have a well insulated house?
5. Have you changed the batteries?

hi OP

1. set at 22 degrees
2. actual temp is 17.5 degrees
3. yes flame symbol is showing
4. yes only 6 years old
5. brand new thermostat and batteries

I assume the original wiring for old honeywell dial type thermostat was red = live, blue = neutral and yellow = switched

i can only assume this is a wiring issue but knowing which one goes to a, b, and c of new thermostat is a mystery to me

cheers

mikeke

 

[D_Hailsham]

1. set at 22 degrees
2. actual temp is 17.5 degrees
3. yes flame symbol is showing
4. yes only 6 years old
5. brand new thermostat and batteries

Do you have a thermostatic valve on the rad controlled by the DT90E?

Have you checked the actual temperature using a separate thermometer?

I can't see how it can be a wiring issue as the boiler does light when you turn the stat down and up again. If the wring was wrong, it would either never light or it would blow a fuse.

Try setting the thermostat to 23 degrees and post what happens. (This isn't a permanent solution ).

 

[Ryansimmo]

Hi,

This is my first post so please be gentle.
i'm having the same issue as above, would someone be able to assist please.
When working it's great but the heating is not automatically coming on in the morning.
The temp is set to 23
Programmer is set to come on at 5am.
Honeywell 3 port valve
Supreme 50l boiler.

Please let me know if you need any further info.

Looking forward to some assistance.