Honeywell CMT927 LCD Display Problems

Main problem: LCD Display Fault. The Honeywell CM927 (CMT927A1049) Wireless Chronotherm Thermostat sits in a higher price bracket than many of its fellow, same brand thermostats. Overall, Honeywell do make great products. They've been in the business for many years and the big majority of their products are very reliable. However, there are some that slip through the net. Sadly, this model is one of them, and as a result, does not have the best reputation with customers. This is mainly due to problems with the display. Which, unfortunately, is not the only Honeywell model to suffer from a very similar issue. The CM907 is also cursed with screen problems. So what exactly is the problem? Well, the LCD screen issues come in many forms.

Fading, jumbled up letters and numbers, partly dead, and total failure. There is also no set time for if / when this happens. It can start to play-up after a few months, or, more commonly, after several years. It should be noted that not all CM927's suffer from issues. Many are just fine, with no issues to report. But, there are a considerable amount of complaints, which translates to many failures overall, and for a thermostat with a high price tag like this, it is a real disappointment. We're not talking about a twenty pound unit here, the CM927 costs over £100 to buy brand new.

The main culprit for the screen failing is moisture getting inside the control unit over a random period of time, causing the gradual development of the screen becoming unreadable / dying. And with this it goes without saying. Unreadable equals the inability to actually operate / program the thermostat, leaving it pretty much useless.

How To Fix It?

There are various methods out there. Some people have put their whole unit in the oven on a low gas mark in an attempt to dry it out. This is not recommended! Others have taken the LCD screen out (quite straight forward) and used either a hairdryer or toaster to heat it up. This method really does work and is the recommended "do-it-yourself" for a quick repair. See the video for exactly how to perform this repair by Handy Hawkins below. He is doing the repair on the CM901, but it also works with the CM927, CM907 and others.

However, most have tried placing it in an air tight bag with silica sachets in an attempt to remove any moisture. Sometimes these methods do work well and the thermostat is fixed well enough to be operated. The success rate is high. How long it stays fixed for though is another matter all together.

These fixes are usually temporary, not permanent. But if one of the methods does fix your LCD, and then after a few months it develops the same problem again, just try the same trick that sorted it out the first time. There's a very good chance it will work again. Saving you the cost of a replacement. In some cases you might not need to take the unit apart.

If you don't feel comfortable taking the display out, you can always apply some gradual, light heat to the front of the LCD screen. Apply clamps or light pressure of some kind. Use a hairdryer, heat gun or toaster and steadily wave the heat on to the display. Once the display darkens a little, test it out. Rinse and repeat if the first attempt doesn't have the desired effect. If all else fails, bite the bullet and open it up. It's not hard to do, as most pieces just clip in / out. Follow the hairdryer / toaster technique and get it up and running again.

I'm no DIYer, I Want My Money Back

Honeywell are well aware of this problem. I'm not sure on the exact time-frame, but if your CM927 (CMT927A1049) fails within a couple or more years, Honeywell should refund you or send a replacement free of charge. Depending on how long Honeywell offer on this thermostat, check whether it is still under warranty. Dig out your receipt if you have one, and take some pictures showing the fault and they should offer you one of the two options above.

If you don't have the receipt, it doesn't necessarily mean all is lost. There should be something on the unit itself which confirms its age / date of issue / manufacture. This should determine whether your CM927 falls within an acceptable time frame (pretty sure its around five years) to justify Honeywell giving you a refund or replacement.