Worcester 35cdi mk2 fuse blowing

[eezergeezer]

hello all,

Hope you can help. As probably understood from the subject.
35 cdi Mk2 F1 fuse keeps blowing when the thermostat is turned up.

background is that the diverter valve as been recently changed and the front facia also replaced.

The bloke that changed it has gone on holiday now so a bit stuck.

I checked the connections for the therm first. I seeing there should be a link between the ST8 Ls and LR ?

the thermo is a Honeywell T6360b theres only 2 connections made from the 1 and 3 terminal.

Which terminals on the ST8 should be used and should there be a link?

Also if not the above prob..Can I unplug all the connections but the power and try to find the fault? go through a few fuses but wortha a shot?

Will the thermistor being faulty be the cause ?

any help much appreciated.
thanks in advance

 

[Agile]

The only things which will blow fuse are mains powered parts, pcb, pump and fan!

Most likely pump!

Try disconnecting it.

Then if need be power it from mains lead and plug with 3A fuse.

Tony

 

[eezergeezer]

forgot to mention I still get hot water.. could it still be the pump mate?

also the fuse blows as soon as i turn the heating on via the thermostat.

I will do the following tomo. unhook the pump and fan leaving the thermostat connected. then turn on... if fuse still blows prob the pcb right?

thanks!

 

[simond]

Disconnect the wiring from Ls and Lr. Insulate ends. Then link Ls and Lr and see if your heating kicks in.

Sounds like external wiring.

 

[eezergeezer]

Fixed!!!

Hello Gents,

Just got to say many thanks to both Tony and Simon,

Tony, I found some more information out after a chat with my ole man.. Something he didnt tell me initially (cheeky git).. After the fascia install the 3 knobs were placed back into the respective holes. One was slightly misaligned and i found out it was forced slightly by the plumber. This caused the variable resistor to break on the circuit board. hence causing a short and blowing the fuse.. it was not immediatly visable however once I opened up and investigated could see the fault. I went down the direct electronics (fantastic little parts shop which sells loads in forest gate) and picked up a new one for 40p... removed the old one cleaned and soldered new one on the board.. No more fuse blowing!!

I then worked out from Simons post i needed to have the thermostat connected to Lr and Ls and the whole thing fired up with no issues!
Neutral was being connected initially as it was blue that was the only reason.......I have since taped a diff colour so in future all will be clear...

Phew.. it was getting a bit cold in the house and we were getting quotes for around £150- £250 to diagnose and fix..

Thanks again!