Combi out of control

[boilerboy]

Scenario: Worcester 240 Combi - controlled via a Danfoss TS75 digital time programmer, set to come on mornings and evenings. No TRVs or room thermostats, temperature controlled only via the dial on the boiler.

Installed a Drayton Combi Stat in the hallway, wired in as per the Worcester/Bosch installation manual.

Here's the problem: If the temperature drops below that on the room stat in the hall, on comes the boiler, regardless of the settings in the time controller. I even tried switching the programmer to the OFF position. Dialled up the thermostat setting - on came the boiler.

I think I have missed something(!), but I can't work out what. Hopefully
someone can point me in the direction of my mistake.

Help...

 

[htgeng]

wired up so boiler thinks its a froststat? double check your wiring again.

 

[boilerboy]

Nope. Think I've sussed it. Had to do an extra, unwanted, bit of dismantling tho.

The timer has two electrical cables coming out. One provides power to the boiler, the other is a 2-wire connection into the room thermostat terminal.

When the timer switches on it has the same effect as a room thermostat activating. Seems to indicate the original installation may have been done on the cheap and cheerful.

Looks like what I actually need is a mains powered, 3-wire 7-day programmable thermostat.

Recommendations please...

 

[breezer]

i would be inclined to agree with other post, you have wired it wrong.

look at it this way, you are saying you need a 7 day timer, no you dont, all a 7 day timer does is to have differnt options for the 7 days, the 24 hour timer you have should be ok, have you tried using the other terminals in your room stat, or has some joker put a frost stat in a room stat box?

to test your wiring, turn mains off, connect the two stat wires together, (turn mains back on) boiler should light, if it does you have stat wrong, if it doesnt you have wired stat to wrong connections on boiler

 

[boilerboy]

So little faith from you all!

My wiring was fine. The time control was wired in to the room stat terminal (see previous post), so when I replaced it with the room stat - no time control.

Sorted now.

Wired the time controller back in, in series with the room stat. 2 switches, one circuit, hey presto.

Thanks to those who responded with advice.