Underfloor Heating Thermostat blowing fuse

[GavinBroomf]

Hi all,

I've had my underfloor heating installed without too much issue for circa 15 years.

Recently I had a fuse blow on the main panel. This had happened once before and I had determined it came from when a certain room thermostat switched the loop to that room on.

I've had that issue previously and switching out the thermostat seemed to cure it.

I've done the same this time, which has involved buying a new thermostat as the old ones are now discontinued. I wired it up as per the thread: https://www.diynot.com/diy/threads/...tead-of-a-ret230.585572/?utm_content=cmp-true

but it's still blowing the main fuse when the room calls for heat.

Can anyone give me a steer on what it might be?

 

[EFLImpudence]

Just to be clear as people often use the wrong names.

Is it definitely a fuse? I am sure it won't be the main one.

Picture of the thing that is 'blowing' please.

 

[GavinBroomf]

Sorry, describing it as "the main one" is probably wrong. It's definitely a fuse, an F4a H250v. It's the one on the underfloor heating circuit board that all the thermostats and valves wire into, hence referring to it as the main fuse.

 

[EFLImpudence]

Ok, then for a fuse to blow, it must be a fault L - N or L - E somewhere.

 

[CBW]

Can you show the wiring for the thermostat?

 

[flameport]

Likely culprit is the thermal actuator for that particular zone.

Thermostat only connects 2 wires together so faults are unlikely there.

 

[GavinBroomf]

Can you show the wiring for the thermostat?

Here is the wiring as was, with the old stat. Worked for years before blowing:

I then, in live with this thread (https://www.diynot.com/diy/threads/...tead-of-a-ret230.585572/?utm_content=cmp-true) rewired to:

I've a couple of spare actuators (Thanks for the official name), so could try swapping that to see if it helps, unless I've done something obviously wrong from these photos.

 

[CBW]

If the same thermostat as linked thread, then seems ok. Could be as per @flameport that it’s an actuator/something else.