swapping out a Potterton prt100 room therm for digital model

[bob127]

Hi,
I am thinking of swapping out my Potterton PRT100's for new digital thermometers.

I've two PRT100's, my heating is zoned upstairs and downstairs.

The PRT100's (see image) are both connected as follows:

1 brown wire
2 brown wire
3 empty

(There is an earth cable but its not connected).




The Honeywell DT90 looks neat and simple (I am only looking for a switch at the moment as I have a programmable panel - Towerchron QE2).

Would the programmable Honeywell CM907 be compatible with my existing programmable unit (Towercrhron QE2) or would they conflict?

I'm thinking of a DIY job, I've read some posts and looked up the wiki.

Thanks, Rob.

 

[mikely]

I'll rephrase that because you have added info and other questions.

 

[bob127]

mikelyThe DT90 is a good choice. It is a modern TPI controller rather than just a simple thermostat and it is simple to install (data sheet available here: http://products.ecc.emea.honeywell.com/europe/ecatdata/pdf_dt90_dt90e1012.html). You just need to identify the live and switched live wires going to your PRT100. You should also find a neutral wire connected to the PRT100, which is not used with the DT90. I found some info that suggested the PRT100 terminals are marked N, TL and H, in which case the connections required will be:

Connect wire in PRT 100 terminal TL to DT90 terminal A
Connect wire in PRT 100 terminal H to DT90 terminal B

You need to have a look to see how the terminals on the PRT100 are marked. It may even have a connection diagram marked inside it.

Back to top

Sorry, but I updated my post with an image while you were posting.

 

[mikely]

The DT90 is a good choice. It is a modern TPI controller rather than just a simple thermostat and it is simple to install - data sheet available here: http://products.ecc.emea.honeywell.com/europe/ecatdata/pdf_dt90_dt90e1012.html.

The CM907 gives you the advantages of programmable temperatures through the day and optimised start. I have one and I would certainly recommend it for flexibility. Yes it would conflict with your existing programmer, but you can just set your programmer to CH permanently on and let the CM907 (or CM907s) do the controlling.

To connect the DT90 or CM907:
connect brown from terminal 1 to A
connect brown from terminal 2 to B

 

[bob127]

Thanks for the advice. Great forum.
I might sway towards the CM907 (x2). It should give me control if the old program panel is removed.

 

[bob127]

I got the CM907's. They installed very easily and are so much better than what I had before. Thanks for your advice and suggestion.

....you can just set your programmer to CH permanently on and let the CM907 (or CM907s) do the controlling.

This is how I am running them.
I have programmed the daily settings (6 of them) but I have to switch off the programmer before going to bed as the heating keeps running during the night. How do I set the cm907's to stop asking for heating around 11pm?

Thanks.

 

[Unklian]

Have your last temperature change at 11pm and
set it to something like 14 degrees or less.
Next morning 6am perhaps, back up to 19 or 20?

Ian.

 

[bob127]

Thanks.