Vaillant 628 thermocompact boiler ( sealed pressurised system)
Drayton 5/2 timer for heating and water + Potterton thermostat + Potterton Motorised Valve.
Hot water heating working ok from timer.
Heating not responding to timer & thermostat.
Thermostat has power, and clicks when manually rotated around sensed actual room temp.
BUT...the boiler motorised valve does not appear to be opening to open the central heating circuit. ( It has a LED showing it's powered)
I can run the boiler in manual for central heating by removing the timer and thermostat as external controls, jumping the terminals in the control panel of the boiler and then manually opening the motorised valve and latching it open.
Where is the problem in the circuit ? Timer, Valve or thermostat ???

steve, February 2009

has power, will not ignite, Vaillant GA92-100

joe tongel, March 2009

Definitely wasn't the thermostat as replaced with a new one and made no difference. Have ordered new actuator for valve.

Steve, February 2009

sounds like could be synchron motor on valve, call from stat should cause valve to motor over, when over sends power to boiler to fire.

tojo, February 2009