Honeywell ST699 Programmer Replacement

Very easy to operate, partly because of using simple, foolproof slider buttons for the main functions, the Honeywell ST699 1 day Programmer has proved to be an extremely reliable product. Of course, with any electrical item, including thermostats, there's always the potential for a problem to arise. And the ST699 is not excluded from this. However, overall it is a very solid unit. If you read through the reviews you will no doubt consistently be reading that the owners of this model have regularly only experienced a fault after 15 - 20+ years of trouble free usage.

The problems after a few decades of use are usually down to general wear and tear, so in some ways its to be expected. Some of the problems on the earlier models, such as a failed back-up battery, can be fixed quite easily. Although it does depend on the exact model as to whether the replacement battery is compatible or not. That's because the earlier models have the capacity to have a new back-up battery fitted (3/v150h Varta). Whereas the newer models have a totally different type of battery installed (A flat cell type) which is also soldered into place.

So really, if you have an earlier model with this problem, its actually better. Because for £8 - £10 you can buy and install the new back-up battery yourself (make sure the electricity is isolated). There are a few other problems that can arise with the Honeywell ST699 Programmer after many years of usage, and some of those include: A few reports of a faulty relay (won't switch off), which was sometimes misdiagnosed and was actually the result of a faulty zone valve rather than a problem with the programmer itself. Testing is required to isolate exactly where the issue is coming from.

More issues: Something has burnt out on the internal motherboard resulting in a non-working system (replacement usually required). Contacts needing to be cleaned. The clock / timer can develop a tendency to reset or change itself. Usually, performing a reset can fix this, but if it keeps happening it may be time to buy a replacement unit.

Honeywell ST699 Programmer Replacement

Whilst its not the cheapest option out there for sale, the best, or smartest replacement for this programmer is to actually just buy the same model again (ST699). This is because its generally a very reliable programmer and lasts so long in the first place. In most cases its also extremely easy to fit, requiring as little as a direct swap with the faulty unit. Take the old model from the back plate and clip the new one into place. And that's it, all done. You could also buy the Honeywell ST799 if you want to upgrade to a 7 day timer rather than a 1 day timer with the ST699. But be aware, from most businesses / online stores selling the ST799, it is more than double the price of the ST699.