"roberth1" wrote in message
...

I have A CH system with gravity HW with a mechanical cylinder stat. and
the heating controlled by a 2 wire mechanical thermostat.
The Controller is mounted near boiler which is not easily accesible.
Gas fired boiler replaced in past 3 years.

Have you considered using a Danfoss TP9 programmer. This is a two channel
programmer, which uses a wired remote room temperature sensor. . The H/W can
have two on periods each day. The C/H can have 6 temperature changes per day.
There can be separate weekday and weekend programmes.

There is a gravity option. In this case the boiler only gets power when either
the pump is running to heat the radiators or during the H/W on periods.

If you have an existing room thermostat, then likely you can replace it with the
TP9's sensor and use the existing wiring to connect back to the programmer
position.

You can download all the details from the Danfoss web site.

I've not found another programmer which works in the same way.

--

Michael Chare