Room stat or programmer blowing switched fuse

[stoatgobbler]

I recently had a new 7 day programmer (Honeywell ST9400c) and a room stat (Honeywell T6620B) fitted to my gravity fed system. These were replacements for older models.
At first worked ok but then the fuse in the switched fuse to the programmer started blowing on operation of the central heating. Did not blow until set the room stat to 21degrees. Replaced fuse(s) and had 2 or 3 days when fuse didnt blow. Has now reverted to blowing the fuse every time I switch the central heating on!
The water heating works fine as long as I dont start the central heating.
Could someone help and advise me pleae? Is this a fault in the room stat or the programmer? or could it be a fault in the pump or a zone vave? No problems till I changed these 2 items.

 

[seco services]

i would check the pump first.

 

[kevplumb]

and second

 

[stoatgobbler]

i would check the pump first.

Thanks. Am I looking for a water leak?

 

[seco services]

water leak
burnt connections
even a seizing pump can keep blowing fuses.

i would remove the plastic top, look for any signs
if ok disconnect the pump wires, make them safe and try system.

if boiler fires etc then check pump for seizing.

 

[stoatgobbler]

would that cause the fuse to blow as soon as heating is switched on and before the pump has time to actually start?
Are you anywhere near Saffron Walden???

 

[seco services]

thats abit to far up for me.

room stat sends signal to valve - then pump/boiler quicker than you can blink.

same if you turn anything faulty on it will blow before you have got your hand off the switch.

 

[stoatgobbler]

Thanks,
How can you tell if pump has seized? Cant see any water.

 

[seco services]

what make is it?
in the centre will be a large screw.
place a cloth under the screw and remove it.
place a flat ended screw driver in the hole and it will go in a slot and you can rotate the pump spindle.

 

[kevplumb]

View media item 667

pics worth a thousand words

somebody said

 

[seco services]

View media item 667

pics worth a thousand words

somebody said

 

[stoatgobbler]

Many thanks.
I will try tomorrow and probably call a heating engineer on Tuesday. I will let you know the outcome.
Once again thanks