Il Mio Problema
The gas central heating did not always turn on when demanded by the timer controls or by manual override (eg add extra hours). It could be forced on either by turning the whole system off and then on again, or by turning the roomstat (Honeywell HCW80) down to minimum and back up again. This mostly worked but not always. The system was getting more unreliable over the first few weeks of the heating season. All led's showed satisfactory lights on the timer, roomstat transmitter and receiver. The hot water control was satisfactory.
La Mia Riparazione
The 15 year old HC60NG receiver for the central heating seemed to be the most likely culprit. I suspected that the contacts on the relay might be dirty ( I could hear it click on so the magnet was OK). To remove this unit from its backplate (after turning off all power of course) press a flat head screwdriver into holes on each side and pull the front of the unit away from its backplate. Detach the circuit board from the front cover by carefully bending the two plastic pins at the top. When checking the big rectangular 0.68uF capacitor (labelled X2 and u68) with a capacity meter, I found it was only 0.27uF ie way outside its 10% tolerance (labelled K). I soldered in a new capacitor and it seems to be working now. Will update if necessary.
Il Mio Consiglio
Note Google's Artificial Intelligence (AI) falsely says that the access hole in the HC60NG is at the bottom rather than the sides! AI is good but not that good yet.
I have changed the X2 capacitors in another Honeywell unit (the ST9400C timer unit) to solve its problem years ago, so am suspicious of Honeywell's lack of robustness in their designs.
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