Digistat 3 to replace old honeywell

[CherokeeDriver]

Hi there. Before anyone shouts at me I have read all of the other posts & FAQ concerning this task. Summary is old Honeywell had 4 wires - Red (Common), Blue (Neutral), Yellow (Call for Heat), Earth. I bought a Digistat 3 in B&Q and from this forum deduced that only need 2 wires - Red (Common Terminal 1) and Yellow (Call for Heat Terminal 3). Trouble is when wired in this fashion the boiler never comes on, even if the Flame i.e call for heat is shown on the Digistat. Out of curiosity if I wired Yellow to port 2 (Demand Satisfied) the boiler comes on continually. Do I have a moody device and need to get it swapped at B&Q? If I put the Honeywell back on everything works fine again.

 

[ricarbo]

It's only a battery operated switch. You could take it off the wall and see if the two terminals will turn on a torch bulb conneted to a battery if you haven't got a multimeter.

 

[CherokeeDriver]

Thanks - good idea. I am sure that the Red (Common) connects from Terminal 1 in the honeywell to Terminal 1 in the digistat. All the advice on here states that Yellow (Number 3 on the Honeywell) should also connect to Number 3 on the digistat. I have isolated the Blue (Neutral) and Earth. so you are correct - the thing should just act as a switch and make the circuit to call for heat. Don't understand why the boiler comes on perpetually when Yellow is in Number 2 - my guess is that the circuit is always closed so regardelss of the Thermostat setting the call for heat is always made. Anybody had any interesting non-standard wiring configurations inside their Timers / Junction boxes etc. I have a Honeywell 7 day timer that has 1 hour override, Off-Auto-Once-Cont settings.

 

[hemclio]

Hi wonder if this is related to my problem.

I took the cover of my thermostat yesterday as i wanted to replace it. I tested all the wires and they were all dead.

I.e. no powere coming to the thermostat at all reardless of how i set the controls on the combi.

Surely the red should be live going into the stat.

 

[CherokeeDriver]

Henclo

Please don't hijack my thread!

Your problem was answered by someone else - the RED / LIVE / COMMON call it what you want only goes 'active' when the boiler / programmer unit is switched on i.e. it is a switched live not a constant live. My system is the same. The problem I have is that when the thermostat has a call for heat (and the boiler has SWITCHED the common on becuase the timer is telling it to operate the Thermostat doesn't close the circuit to call for heat. Confusingly if I wire the call for heat into the No 2 terminal the circuit is closed perpetually and the boiler comes on regardelss of a call for heat being made or not.