Heating wont turn off

[MartyMalabu]

First of all, just to mention that I changed the cable from the cyl stat to the airing cupboard connector block (brand new 4 core with the earth clipped back at each end), and the fault is still there. I am seeing 30v-80v (cyl stats down - cyl stat up) on the T1 wire even when disconnected at BOTH ends. This changes to 0v-50v sometimes, and I think this is when HW is ON, because the 30v floating on the HWOFF line drops away. So I have a stepped voltage between 0v to 80v on T1 depending on whether HW is on and depending on the cyl stat position.

This makes no sense at all!

To recap:

1. You have replaced the cable from cylinder stat to the terminal strip

Yes

2. If you disconnect the wire from cylinder stat T1 at both ends (i.e at the cylinder stat and the terminal strip) and then measure the voltage between the disconnected wire and neutral you get 30-80V!!

Yes

or do you mean that you get 30-80V on HW cylinder T1 with the wire disconnected?

If so what do you get on C terminal and T2 terminal?

What voltages do you get on the three HW stat terminals when the wire to T2 is also disconnected?

I am seeing the following voltages, but am convinced that when connected up, the boiler switched live is giving some strange results.

No Call from programmer, room stat turned down

cyl stat turned down
C= 240, T1 = 47, T2=240
cyl stat turned up
C= 47, T1 = 47, T2=240

Now disconnect feed to boiler switched live

cyl stat turned down
C= 240, T1 = 0, T2=240
cyl stat turned up
C= 0, T1 = 0, T2=240

Boiler switched live wire (disconnected from chock block) =98v
When reconnected to T1/Orange = 47v

Is this looking like a pcb fault ?

 

[D_Hailsham]

2. If you disconnect the wire from cylinder stat T1 at both ends (i.e at the cylinder stat and the terminal strip) and then measure the voltage between the disconnected wire and neutral you get 30-80V!!

Yes

So you are getting a voltage on a wire which is not connected to anything! That's impossible - unless it is being induced in the wire!

I am seeing the following voltages, but am convinced that when connected up, the boiler switched live is giving some strange results.

No Call from programmer, room stat turned down

cyl stat turned down
C= 240, T1 = 47, T2=240

cyl stat turned up
C= 47, T1 = 47, T2=240

In both cases C should be 0V if the programmer is HW OFF

Now disconnect feed to boiler switched live

cyl stat turned down
C= 240, T1 = 0, T2=240
cyl stat turned up
C= 0, T1 = 0, T2=240

C is getting 240V from T2 when the stat is turned down

Boiler switched live wire (disconnected from chock block) =98v

That definitely is wrong - should be 0V

Is this looking like a pcb fault ?

Possibly, but the next thing to do is check at the boiler.

Disconnect the switched live from the Ls terminal and measure between Ls and N. It should be 0V.

Then reconnect the wire and check again.

Incidentally what are the Reset and Burner LEDs doing when you measure the voltage on Ls?

 

[MartyMalabu]

Boiler switched live wire (disconnected from chock block) =98v

That definitely is wrong - should be 0V

Is this looking like a pcb fault ?

Possibly, but the next thing to do is check at the boiler.

Disconnect the switched live from the Ls terminal and measure between Ls and N. It should be 0V.

Then reconnect the wire and check again.

Incidentally what are the Reset and Burner LEDs doing when you measure the voltage on Ls?

I did these measurements 2 or 3 posts back...

This is with both stats down, and neither HW nor CH calling from the programmer...

SL to Neutral on the boiler = 47v

I removed the feed to the switched live at the boiler, and the end of the wire was 0v, and the switched live connector now measures 122v . Refitted wire, voltage reads 47v again.

There are no error conditions showing on the LEDS

 

[D_Hailsham]

This is with both stats down, and neither HW nor CH calling from the programmer...

SL to Neutral on the boiler = 47v

I removed the feed to the switched live at the boiler, and the end of the wire was 0v, and the switched live connector now measures 122v.

Refitted wire, voltage reads 47v again.

So the source of the voltage must be the SL terminal of the boiler. Which points to the PCB as being the culprit.