The receiver unit (that connects to the boiler wiring) for all the later versions of this wireless thermostat are the same, the trarnsmitters, with the LCD display are different. Most receivers suffer from a common fault which is the large capacitor (0.68 micro Farad) on the circuit board developing an increased Equivalent Series Resistance (ESR). WARNING: UNLESS YOU HAVE ELECTRONIC KNOWLEDGE DO NOT ATTEMPT TO REPLACE IT. It is a special type (X2) designed for safe connection across the mains. Electricaly equivalent items from most component supply shops I tried are physicaly too thick to fit in the box and I found that only the exact type originaly fitted will suffice. These are difficult to obtain.
In my opinion, the circuit design is very poor, as this capacitor is used to reduce the AC mains voltage from 230V to approximately 24V. As the capacitor becomes defective with age, this voltage drop increases and when a signal is received from the thermostat, causing more current to be drawn from the mains, only 9V or less is available to operate the switching relay on the circuit board, which needs 15.6V to energise.
Hope this helps someone with electronic knowledge and discourages others to try and replace the capacitor.
Kayball
May 2010
(from http://www.howtomendit.com/answers.php?id=49588 )
David Bed, September 2011
