Fuse spur switch won't turn on after replacing Honeywell ST9400C

[Mense]

It was a like-for-like replacement (with a new ST400C) where the old one was taken off the back plate and the new one slotted in (without touching any of the wiring), but just as the new one slotted into place, the fuse indicator light on spur went off and the boiler switch in the fuse box tripped. I have since changed the fuse in the fuse spur socket twice with new 3A fuse (same as before), but it won't switch on. The wiring in the backplate is in tact. The wiring in the fuse spur socket is also in tact.

Any ideas what could be the problem.

 

[jj4091]

If you are changing one ST9400 for another then from your description it must be faulty as you appear to be putting a short across live and neutral or earth. Are you sure the old one wasn't a slghtly different model that requires wiring to different terminals as shown in the instalation instructions

Replacement Wiring
If using the ST9400 to replace other Honeywell Programmers, the equivalent wiring terminations are shown in the tables below.
ST6200/ST6300/ST6400 L N 1 2 3 4
ST9400 L N 1 2 3 4
ST699/ST799 L N 3 4 5 6 7 8
ST9400 L N 4 2 not connected 3 1 not connected
ST7100 L N 3 4 5 6 7 8
ST9400 L N not connected 2 4 not connected 1 3
ST7000A L - 2 3 4
ST9400 (see notes 1, 2) L N 1 3 4
Notes: (1) A permanent mains supply must be provided for the ST9400 Programmer.
(2) ST9400 must be confi gured as a Mini-Programmer

 

[Mense]

Here are the pics of the old and the new. The first programmer is the old one, the other is the new (well new in the sense it was bought in the last few days but not brand new).Third pic is wiring as it is with existing programmer. The wiring hasn't been touched. Reason for replacement is the text on the old one is extremely faded and the buttons require a lot of effort to turn on and off and switch between different options on the programmer.

Just below the backplate there is a relay box (Honeywell) and right of it the fuse spar switch

 

[dilalio]

Checked your circuit breaker?

 

[Mense]

All the switches on the circuit breaker are on

 

[CountryFan]

You say the wiring hasn’t been touched, yet on your wiring picture:

There is no neutral wire in the N

You have a CH off (blue - I suspect this is the N) and this screw looks more prominent than others

 

[dilalio]

All the switches on the circuit breaker are on

Guess you don't have a multimeter.

 

[Mense]

Here is a clear pic of the wiring

 

[Mense]

I have one of those electricity testing pens but not a multimeter

 

[dilalio]

You need a neutral... And an earth really.

 

[dilalio]

Stick the blue in N

 

[CountryFan]

Here is a clear pic of the wiring

Put as many as you want up. You still have no neutral and still have a CH off - which is rarely used

 

[CountryFan]

Stick the blue in N

Or at least renove it and see if it still trips

 

[Mense]

I had the two programmers switched by a builder (he also works with electrics when he needs to). I am sure he didn’t touch or switch any of the wiring around. I was away for a while when he was replacing them. I can’t be 100% sure simply because I wasn’t there when he did it and I hadn’t taken a picture of the wiring before he replaced the programmers.

 

[CountryFan]

I had the two programmers switched by a builder (he also works with electrics when he needs to). I am sure he didn’t touch or switch any of the wiring around. I was away for a while when he was replacing them. I can’t be 100% sure simply because I wasn’t there when he did it and I hadn’t taken a picture of the wiring before he replaced the programmers.

Finally, a bit of sense. As I said, you have no neutral and a CH off. Inform the builder he has done it wrong. If it was swapped on the backplate, the replacement would work unless faulty.