boiler wont turn off, by control panel

[magrumbles]

my daughter has a potterton netaheat conventional system, with 2 tanks in loft and hot water cylinder. recently came home to find system not working. traced problem to a blown fuse in wiring panel . repleced fuse, 2 amp, boiler started but blew fuse in 2 seconds. byprocess of elimination found if disconnected pump , boiler started and fuse did not blow. replced pump with grandfos type. and all seamed well, apart from no hot water . moved diverter valve for hw manually hot water flowed heard lever returned under spring pressure. but now pump seems to work continually with boiler kicking in from timt to time. even with control panel set to hw and ch off. only way to stop it is to turn off mains supply. any ideas.

 

[tamz]

Sticking microswitch in valve. If you don't know or can't figure out how to get to it change the valve.

 

[magrumbles]

Thanks! Is that expensive or a difficult job?

 

[Puddle]

If it has a removable head,you can just replace that on the old body or if you have to change complete valve ,will have to drain down past valve to do so

imho

 

[magrumbles]

Thanks! Silly question but how can you tell which type it is?

 

[Puddle]

What make of valve is it,if honeywell it has a bobble on the end of the head can be removed and if thick red pad between valve and head you have to replace complete valve

 

[magrumbles]

It is honeywell. We did some investigating last night and it was an electrical fault. There was one strand of wire from the yellow/green wire touching another. My Dad move the strand and the pump/boiler stopped. One of the valves does look like it might have been the fault as it was all rusty, but reading other threads, we could feel the pressure trying to move the switches manually on the valves when the system was off. We have tested the controller box and the pump/boiler now stops when both H/W and C/H options are off. Thank you to everyone for replying! Must appreciated.