Replacing Mechanical Thermostat with Programmable Thermostat

6 Jan 2009
Reaction score
United Kingdom
I have an existing Ferroli boiler which has the small round programmer (1 day only) with a mechanical room thermostat. Is it possible to replace the room thermostat with a digital programmable thermostat to enable better control of the boiler. In essence I want to set the boiler to be on permanently and then use the digital programmable thermostat to control via temperature the need for heat. I hope this will enable me to gain 7 day control of the boiler.

Question is, is this possible and do the digital programmable thermostats work as a switch with a single 2 core wire similar to mechanical thermostats. I am looking at the 3 models below:

Danfoss TP7000
Drayton Digistat 22084
Honeywell CMT907

Any comments or pitfalls gratefully received.
Sponsored Links
Digital programmable thermostats usually have a simple changeover switch, so people can use them for heating or cooling.

Be aware that some also need a mains neutral feed, unless they are battery powered like the Horstmann one.
You may not have this on your old unit, unless it has an accelerator resistor fitted.
Horstmann one below.

If you read the user reviews on this one, they tell you how to connect it.

Replacing a mechanical room thermostat is quite easy, some will even fit into the same space as the old one.
The Honeywell CM907 is probably the better and can replace the existing mechanical stat with no problems as it is battery powered. As you thought, the existing timer should be set to continuous.

If you post the make/model of the existing stat, I will tell you how to wire the CM907.
Thanks for the advice, willl be removing the cover on the existing stat to see how many wires there are. Will post the make and model of stat and boiler at the same time.
Sponsored Links
The existing mechanical thermostat is made by Honeywell, however I cannot find out how to remove the cover and see what is inside. It has a brown backplate and a greeny grey exterior, there is a screw in the top right but removing that does not seem to allow the cover to be removed. I have posted a picture, does anyone know what make or model it is and how to remove the cover?


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local