Central Heating Pump running constantly

Hello

We had a new central heating system installed about 3 years ago and it has worked well with only the radiators needing bleeding every now and then..it has a Boulter boiler, 17 radiators and is a sealed system.

My problem is to do with the Pump which is running constantly..it has only recently started doing this (about a week ago) and will only switch off by turning off the main supply to the control panel..it is a 3 speed WILO Gold 60 pump and responds to the speed adjuster slowing down or speeding up when the control is turned..it just wont go off. changing the settings on the controller has no effect it just runs constantly whether the heating/hot water is on or off..we dont appear to have any other problem with the system other than the two radiators which are furthest away from the boiler take an age to warm up..I have recently re bled the system and there is no air to speak of in the system...all radiators bar one have thermostatic valves...any suggestions as to where the problem lies gratefully received..I have contacted a plumbing and heating engineer but everyone seems booked up for weeks

many thanks

Mike

Common problem, is the pump wired back to the boiler? If so, pump overrun is faulty, check/change pcb/thermistor. If not, is there a remote pump overrun controller fitted normally to a junction box, the box where all your htg/hw wires go to.

Furthermore does the boiler ignite when pump is running with no demand from the timer? If so, suspect diverter valve.

ive had faulty diverter valve heads/actuators cause this problem in the past

Edited cause I never read the OP properly.

where is the boiler fitted-im thinking about a froststat..........

where is the boiler fitted?