Tuesday, 2 May 2017

Honeywell CM907 Wired 7 Day Thermostat

For controlling things like Combi Boilers, the Honeywell CM907 (CMT907A1041) generally does a great job. It has many impressive, but these days expected features, including a nice blue LCD (Lot) screen and the all important 7 day programmable function with up to 6 different time and temperatures changes per day. It also has a feature which allows it to update itself when the clocks go forward or back, so the time is not going to be wrong an hour forward or back. Burner icon, volt free contacts and the ability to set it to auto, manual, override and completely off are also present.

Most of these features are basically "standard issue" with a lot of thermostats that fall within the same price range. One plus is that the CM907 is very simple to get up and running. For most people (depending on your system), a quick swapping of a few wires, 2 to be exact, and you should be good to go.

However, there are a few areas of concern with this model. Various problems have been reported regarding the longevity / reliability of this model. Which is a shame because Honeywell generally make great products, lots of them last for well over 10 years. Most people expect a thermostat to last at least a decade, but this one has some users needing to replace it within a few years.


The main problem area appears to be the LCD screen. For some users, after a few years of use it starts to fade, or parts of the screen fail entirely, leaving the owner unable to see the digital readout in order to modify the heat / thermostat settings to change anything. So it basically ends up being unusable. The problem however, doesn't seem to be the actual glass screen itself, but the connections which attach it to the board inside the unit.

This middle joining is known as the ribbon, and its widely reported that it is the heat bonded attachment that is the weak link here. This can be fixed, but will obviously involve opening up the unit and trying to repair it yourself. Thankfully, if you have a Honeywell CM907 (CMT907A1041) with this issue you probably won't need to go opening it up. In most cases, Honeywell do offer a free replacement, as it seems this problem was was the result of a faulty consignment. Not all units were affected. How widespread the problem was is still unknown.

Best price for this model? There are many outlets / merchants that stock this unit. It depends whether you want to buy brand new or second hand. Looking for used, try eBay. In fact, I was just looking on eBay for them brand new and can see quite a few for sale at £40! That's a bargain. Need help with your 907? The Manual is readily available to download or view online. Just search for Honeywell CM907 manual. Or replace the word manual with the word instructions.

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