CH good but no HW with Ideal boiler and Honeywell ST7100

[daylyt]

The system worked perfectly with no disturbances, annual service 3 weeks ago, suddenly the HW to the main house failed. House and extension fed from one Ideal Mexico with individual/independent Honeywell ST7100 progs. Honeywells cross installed to check integrity, good, all red light selections work but HW selection man or auto prog does not initiate boiler. System Honeywell motorized valve checked in man and auto, no solution. Is it a cylinder stat failure or something more sinister?
Immersion heater is providing HW but eating electricity! Any reasonable idea pursued, thanks!

 

[45yearsagasman]

Possibly the synchron motor in the hw zone valve has failed.Easily replaced if thats the fault.Moving the lever to manual is not enough to close the internal microswitch.You can get hot water when the heatng is on by manually turning the hw zone valve.I'm assuming you have 2 zone valves (S plan)?

 

[daylyt]

Thank you very much for the synchron motor idea, but things have gone from bad to worse. CH now has a mind of it's own, currently not functioning after an initial one hour burst, and swapping Honeywell progs again cannot make the house system work, although the house Honeywell prog works the extension perfectly. Are we now looking for a common link between CH/HW for the house, assuming now that the ST7100 is serviceable? Could that be the synchron motor? Seriously confused of Norfolk!

 

[daylyt]

Further to your reply question, the single storey house CH/HW plumbing has one motorized valve for each system and no room stat for the CH system, relying on individual TRVs . The HW is controlled by the cylinder stat with overall timing planning in the ST7100.

 

[45yearsagasman]

I would take a good look at the house heating zone valve and see/hear if the motor is opening the valve fully and therefore activating the end switch.The timer should put 240v to the brown wire and the motor should open the valve fully and th orange wire becomes energised and switches the boiler and pump on.To do these tests you need a multimeter(adviseable) and some skills in checking wiring.A good heating engineer would ID fault in 30 mins.The fact that you have no room stat makes the system simpler.