My previous description of symptoms was incorrect. The valve does not stick and its number is immaterial.
From cold: when power is supplied the valve opens, the extractor fan starts after ~20 seconds and the gas is ignited after ~30s. After ~ 2 minutes the gas is extinguished but the valve...
Thank you D_H. The valve was fitted ~38 years ago and does not have the bump. I have already stripped it down and have cleaned the cog on the servo motor and on the ratchet. I will now lubricate the spindle as you suggest and report.
A query on a gas fired CH and HW system with honeywell V4043H motorized valves. The CH works fine, so does the HW when the system is switched on from cold.
When the water warms up, the HW valve sticks in the open position. The electrics must be ok. Do I replace the whole valve?