Issue with ST9400C programmer

[Kgahan]

Hello. I have an issue with my Honeywell ST9400C and would appreciate any advice. I have set the Heating and Hot Water to come on at the same time in the mornings - unfortunately the Hot Water comes on but the heating is overridden. The heating light comes on (on the st9400c unit) but the pump does not kick in. The heating does work independently as I have it programmed to come on in evenings (without hot water). I can't find any info anywhere to tell me the two can not be used at the same time. The control valve is set to automatic. The thermostat works fine and is set to a high enough temperature to switch heating on.

Any help much appreciated.

 

[Dce]

A lot of these units are faulty. I found tapping the top right hand corner where the relays are, could force them to open. Also turning off the backlight helps more power to go to the relays. Faulty units are from week 37of2010 and week 39 of 2011, but my unit was 2009 and was still faulty. They are date coded eg 1037 on the lable and in software, press + for 8sec.I checked the coil voltages for the 45v relays and they were on only 27.5v but did click on, however when turning on the second relay the voltage dropped to 19.9v which didn't turn on the second relay. Turning back on the backlight further reduced the voltage to 14.8v. So I guess the fault is with the power supply although new relays may be more forgiving?
I did check a newish st9400c and it did give a stable 45.5v dc, suggesting it is the power supply that it's faulty and not the relay. Anyone know how to repair the 45v dc power supply, so I can get the heating and water on at the same time like it used to?

 

[simond]

The relay problem affects both HW and CH. As described, they don't work together but do independently so I'm going to guess this system has a three port valve.....