Central heating controls

[Odd job bob]

Hi, having difficulty getting my head round a central heating wiring issue. I have a Drayton LP711 single channel time switch with a Honeywell DT90E thermostat and a powermatic gas warm blown air heater.
The powermatic has only 2 wires ( control circuit) and the thermostat is 2 wire. How do I connect it up ?, any help greatly appreciated.

 

[ericmark]

Drayton LP711 instructions

and Honeywell DT90E thermostat manual so something like this

 

[Odd job bob]

Thanks for the reply, I forgot to say the boiler is 0v. Am I right in thinking if this is the case there will be no need for the L link to the common 1.
Would it work if I wire it
Wire from boiler to timer term 2
Timer term 3 to stat term A
Stat term C to boiler wire

 

[CBW]

What do you mean by 0v? Where are you measuring? Are any existing controls in place?

 

[Odd job bob]

I am just assuming it’s 0v going back to the boiler because if a join them together the boiler runs.

 

[Odd job bob]

I have L and N at the boiler and 2 control wires from the boiler.

 

[CBW]

Probably need as Eric has done then, just make sure your switching (control wires) are the correct voltage, eg mains or 24v.

 

[stem]

Most warm air units need a permanent electricity supply so that the fan can continue to cool the heater after the programmer / thermostat has switched off the burner, and the control wires are separate to that. Which sounds to me like what you have...

I have L and N at the boiler and 2 control wires from the boiler.

The installation manual for your specific model of heater should provide the necessary information with regard to connecting external controls. If the control wires to the existing thermostat are 230V. One should be a permanent 'live supply' and the other the 'switched live', in which case, the permanent live can be used for the programmer L.

If you determine that the control wires are 230V 'permanent live' and 'switched live' [The installation manual for your specific heater should provide this information] then it could be connected as below.

I've shown the programmer receiving its live supply from the heater because there can be an internal fuse for the control circuits. Sometimes warm air heaters require a 13A fuse for their supply which is too high for the control circuits. But you would need to check this is the case for your particular heater.

If the control wires are not 230V or you're not sure it can be connected with the control circuits isolated from the 230V supply. The 230V supply to power the Programmer will need a separate connection to a suitable supply fused at 3A or less. Note that in this instance there is no link between the 230V and control wiring.

 

[Odd job bob]

Stem
Spot on with your second diagram.
I had already got it sorted by sitting down and drawing the circuit.
Thanks again.