Honeywell ST9400C Programmer Switching Fault - Gives Hot Water or Central Heating not Both?


Postby dce52 » Mon Aug 03, 2015 7:46 pm

The programmer either gives hot water or central heating but not both. I can sometimes get both on it I tap the top right hand corner where the relays are. It also performs better if I turn off the backlight. The relays are energised with 48v but the unit only delivers 28v or 20v with both hot water and heating on and only 15v if the backlight it's on as well. Should I replace the relays with 24v ones (omrom g5la-1) or can I repair the on board power supply? It used to work when it was new about 4 years ago.
There are two 6mm dia 7mm high components on the PCB marked 961 22 63e with a black edge, are they the power supply?
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