Honeywell ST699 tripping RCD when sliding CH switch

[DaveD1977]

We have a back boiler controlled by a Honeywell ST699 programmer (CH & HW). The CH has been switched off all summer, with the HW continuing to be run as normal.
I've just tried sliding the CH slider switch to turn on the CH, and it's tripping the RCD. I turned off the CH slider, reset the RCD, tried again and the exact same thing happened. Before resetting the RCD, I tried turning on the CH using the slider whilst the electricity was off, attempted to reset the RCD - and it wouldn't reset (i.e. it kept tripping). I've turned off the CH slider and reset the RCD so that we have electricity again.
I guess it's a programmer fault as the RCD is tripping the instant I move the CH slider. Has anyone come across this before?

 

[martygturner]

it might not be the controller, it could be the pump or motorised diverter that has a fault, when you turn on the CH that fault becomes live and trips the RCD.

 

[DaveD1977]

We have a back boiler controlled by a Honeywell ST699 programmer (CH & HW). The CH has been switched off all summer, with the HW continuing to be run as normal.
I've just tried sliding the CH slider switch to turn on the CH, and it's tripping the RCD. I turned off the CH slider, reset the RCD, tried again and the exact same thing happened. Before resetting the RCD, I tried turning on the CH using the slider whilst the electricity was off, attempted to reset the RCD - and it wouldn't reset (i.e. it kept tripping). I've turned off the CH slider and reset the RCD so that we have electricity again.
I guess it's a programmer fault as the RCD is tripping the instant I move the CH slider. Has anyone come across this before?

Ah, OK - thank you. In which case I guess it's best to call a plumber rather than electrician to take a look?

 

[Madrab]

Probably a pump issue, the HW will probably be fed by 28mm gravities so the pump doesn't run. So if the pump's been off all year then it could have seized up or shorted out and now when being powered up it's causing a short.

 

[martygturner]

Ah, OK - thank you. In which case I guess it's best to call a plumber rather than electrician to take a look?

plumber

 

[DaveD1977]

The plumber has been and said it's 99% likely to be the pump. He's said for me to find the pump and he'll then come back and take another look (rather than paying him to hunt for it). I've taken off the boxing in to the left of the fireplace, taken up the floorboards in the bedroom above and emptied the airing cupboard. I can't find it anywhere.
Would anyone have any clues?
Photos attached.

 

[martygturner]

where is the boiler ? do you have a back boiler on the fire ?

 

[DaveD1977]

where is the boiler ? do you have a back boiler on the fire ?

Yes, back boiler. Baxi Bermuda 45/4M

 

[Madrab]

I've seen them in all sorts of places, under floors etc. Easiest way I've found to do it, if there's no apparent locations on visible pipework, would be to try and follow the cabling from the programmer or worst case the boiler connections if that's where it's wired from, it has to hit a wiring centre or the boiler connections block at some point, from there it would have to head to the pump.

 

[DaveD1977]

I've seen them in all sorts of places, under floors etc. Easiest way I've found to do it, if there's no apparent locations on visible pipework, would be to try and follow the cabling from the programmer or worst case the boiler connections if that's where it's wired from, it has to hit a wiring centre or the boiler connections block at some point, from there it would have to head to the pump.

OK thanks. The controller is on the right hand side of the fireplace / back boiler. There's a cable disappearing under the flooring there along with another 2 pipes. I guess the next task is to lift the floor and floorboards to see where that cable goes?

 

[RandomGrinch]

...and genuine question to the RGI's, if a ceramic radiant is missing from a gas fire, would that fail a gas safety inspection?

 

[Madrab]

I guess the next task is to lift the floor and floorboards to see where that cable goes?

Yup, chances are if it's on the wall beside the fireplace then it'll connect direct to the wiring block on the back boiler and then off to the pump.

would that fail a gas safety inspection

It should - it's obviously a defect and using a fire without one would contravene it's safe use.

 

[DP]

plumber

Heating engineer.

 

[DaveD1977]

Yup, chances are if it's on the wall beside the fireplace then it'll connect direct to the wiring block on the back boiler and then off to the pump.
View attachment 355503

In my simple thinking, just because the cable disappears under the floor on the right hand side of the fireplace doesn't mean that's where the pump is. I would imagine that the pump is more likely to be on the left hand side of the boiler where the water pipes exit. I just want to be a bit more logical before I start lifting my vinyl flooring /cutting the plywood / cutting the floorboards!
What do you think?

 

[Madrab]

Of course but unfortunately, invariably there is little logic to where some of these items are placed. Space will be a defining factor, as it's open vent then the placement of the feed and vent may also have defined things.

Yes, of course following the pipework will also lead to the pump eventually.

You say the pipes exit left but the flow and return on a Bermuda exit/enter the right hand side of the boiler. Those pipes where the programmer is may be the mains flow and return and as they are on the right hand side and where the cable runs, that would probably be the place I'd start.