I have a Glow Worm Ultimate Boiler which has a control unit with the following code ULT 100F(its about 10 years old).

The problem is that when the system is off (e.g. no hot water or heating required) the pump continues to circulate water in the system and will continue to do this until the knob on the control unit is turned fully off and then on again. Does anyone know why this is happening and what the cure is?

Details - The boiler just about keeps pace with our heating needs, but has recently stopped switching off the pump. The pump will run all night unless the control knob is turned to off and back on again. The control unit knob is normally set to 3/4 on. This can be set to zero if the boiler is left off for long periods. There appear to be three water circuits: (1) radiators, which is controlled by its own valve. (2) hot water, which is also controlled by its own valve. (3) a redundant and permanently open circuit which appears to relieve the pump flow when the other valves are closed.

Keith, January 2009

hi keith sounds like your actuator switch is broke(it should be labeled actuator on the unit) it is a box with a motor inside the size of a childs hand this is attached to a central heating pipe. it controls a valve to your heating and water. best way to check if it is working is to locate the actuator the switch is on the top of the unit take a note of where the position of the switch is now turn on your heating the switch should move position and stay there if it keeps moving back and forward every 30 secounds approx its broke but if it does stay in place turn the heating off again and the switch should move back i suspect it wont which is why your heating is staying on after you have switched it off if i am right you will have to replace the whole unit which is £30-£40 for the part

:), January 2009