Central Heating/Hot Water control problem

30 Nov 2019
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United Kingdom
Hi All,

I'm wondering if anyone has any idea what is happening here.
I have a CH/HW system made up of Worcester Greenstar boiler, 5 radiators and hw tank controlled by Danfoss FP715Si programmer and Danfoss Thermostat (RF). Programmer is set to run All Day from 0630 to 2230

Over the last year There have been 2 instances (about 4 months apart) where the programmer has not turned off the system and it has gone out of control (boiler running and temperature rising). The screen of the programmer is blank but the 2 "on lights" are lit and the RF unit shows thermostat light "on". I have turned the power to the system off then on. This resets the system and operation returns to normal (off, since I discover this about midnight because we are very hot in bed). The system then runs OK until the next time.

I'm not familiar with CH systems so at am at a loss as to what to do. My initial thought is to replace the programmer as it seems the fault is there. It is a problem that I can deal with while I'm home but obviously could have serious consequences if we were not at home.
Any thoughts ?
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It does sound like the programmer, they have a battery in them and it might be goosed.
The only battery in the system is in the thermostat unit that sits remotely from the programmer and talks to the receiver (RF Unit) next to the programmer. The thermostat has an indicator that shows if battery in need of replacement. The indicator is off, so assume battery is OK. The programmer does not have a battery.
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FP715Si programmer

The Si in the part number stands for service indicator. So that you can pay someone to come out and press some buttons.

If it's been over a year since that has been done, it maybe possible that the programmer maybe making things unpleasant for you to remind you. (so you pay someone to come out)
Google the instructions for full details and how to reset.

It's does sound more like the thermostat problem to be honest though, but worth being aware

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