Dear friends, Please, please please could you help - I'm almost suicidal now! Moved into new house (its only 10 years old) with a sealed heating system. S plan, Drayton valve for heating and Honeywell for water, new simple Drayton RTS2 thermostat in the hallway and a programmer. 31 October, the grundfoss pump constantly ran all night (causing boiler to constantly fire up too) until I switched the boiler off at the mains. called British Gas and they changed the Drayton heating acutator and the room thermostat Everything running fine. 21 November had a new boiler fitted - Vaillant 418 ecotech plus (using existing myson programmer and thermostat) so a straight boiler swap, everything running perfectly. Heating on constant and water on timed. 7 December woke up to the sound of the pump running constantly again, boiler being called for heat until I switched the boiler off at the mains. The installer came - the boiler is working perfectly - he advised that it would chargeable work to locate the fault as he only installed the boiler and this was something to do with the external valve, pump etc.Called British Gas who changed the Drayton actuator again. All running fine, heating on constant (due to elderly father who needs a warm environment due to health condition) and low and behold 48 hours later the pump is running constantly again, firing the boiler up too. British Gas been out earlier today and checked all the wiring in the programmer, the thermostat and the wiring junction next to the heating cylinder, no apparent fault. The Honeywell water valve all running fine too. BG engineer was here for nearly two hours, and disconnected the the orange wire on pump/boiler wires and brown on valve and reconnected them all again. Fingers crossed it may have been a loose wire/ faulty connection as all appears to be working fine now. I'm worried now that why does this keep happening - clearly not the boiler, as it's a brand new boiler but still the same issue of the grundfos pump running all night has happened again!! I was thinking of having a hive installed, but I've enough on my plate with all this!! Apologies in advance for the long detailed post . Any suggestions my good people please?