Newbie Central Heating Problem - HW OK but no CH

[kawum747]

Hi,
Some facts first:
Boiler Potterton Netaheat , Potterton EP2000 Timer, 2x Motorised Valves from Honeywell, Randall? Circuit board
- problem appeared about a week ago but disapeared again for short time and is now permanent
- The pump, boiler work fine for hot water but do not start for Central heating.
- Valves are opened fo CH as well as radiators get hot when hot water production is on. I also checked the valves by removing cover and they open and close ok.
- measured phase on circuitboard for following scenarios:
CH timer on and room thermostat to max > Got phase from timer for CH and thermostat. Pump and boiler no phase. Pump and poiler should come on now.
CH Timer on and HW timer on and room thermostat to max and water in hot water tank cold > Phase for timer for CH and HW an Thermostat and Pump and boiler .
The question is why does the boiler and pump not start when system is in CH mode only although the thermostat and timer are giving a signal to the board.
Could it be that the circuit board is faulty? I did not rip it off the wall yet.
If it helps I could post wiring plan of circuit board.
Thanks for any help.
Regards

 

[kevplumb]

is the curcit board in a grey box on the wall ?

 

[ChrisR]

CH timer on and room thermostat to max > Got phase from timer for CH and thermostat. Pump and boiler no phase. Pump and poiler should come on now......................

The question is why does the boiler and pump not start when system is in CH mode only although the thermostat and timer are giving a signal to the board.

The power to the boiler doesn't come from the timer or stat, but from a switch inside the motorised valve for the CH.
Sounds like the valve is opening, but not far enough to operate the switch inside.

The valve's switch wires are orange and grey, practice differs on which is connected to permanent live and which to the boiler as "Switched Live".

When CH and HW are on, your rads will get warm because the valve is opening to CH, and the switched live from the HW valve is turning the boiler on.

See S plan:
http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.2 S Plan.pdf

 

[kawum747]

Thanks a lot for the help.
Kev: No grey box, but brown with white cover.
Chris: I think you found the issue. Valve switch seems to be the problem. I took one screw that holds the switch in place out and some plastic came off. Looks like the switch is no longer in the correct place. However I opened the valve manually and pump and boiler came on, must have sliped into propper position. Could be as you thought that motor does not open the vave wide enough. I will take it apart tomorrow, bit late now. I will post update tomorrow. Is it worth a try to repair the electric valve or better to get a new one straight away?
Best Regards