Boiler with only l-n-e

growler · Jul 7, 2017

I had to extend a flex for a boiler today that was being relocated to an opposite wall, the flex was only 3 core and the boiler only had live , neutral and earth terminals . I've only been doing heating on new builds for about 10 years and not come across this as usually have a permanent feed and S/l. They are considering renewing the boiler and I'm worried that the current 3 core might not work with a modern boiler. The house was built in 1999 so the boiler isn't that old. I'm only used to s plans and combi wiring , can some shed some light on my problem if you can understand my waffle.
Thanks

Octopus · Jul 7, 2017

"most" boilers need SL, L, N & E these days .... but not all.

Only the MI could inform you properly and not all plumbers understand this... the FIL's boiler was changed .......... the muppet used L, N & E despite the MI saying it needed SL, L, N & E

Ian1981 · Jul 7, 2017

Sounds like an old gravity fed system tho that's usually with A back boiler type

Leesparkykent · Jul 8, 2017

Most boilers will require LNE and SL the only newish boiler I've done over the last few years that only needed LNE was the Baxi solo which I believe has now been discontinued. The Baxi solo had no digital display or pump over run. Most heat only boilers nowadays need a perm live as they have pump over run. So you need LNE, SL and Pump live.

LankyWill · Jul 8, 2017

It might have a wireless receiver as standard, I was quoting a job that had a strange Spanish Combi boiler that only had LNE but used an inbuilt wireless receiver to trigger heat. The thing was the wireless programmer was absolute tosh and soldered directly to the pcb. Customer had to lump it or buy a new boiler.

dksanders · Jul 8, 2017

A lot of older boilers without Pump Over-run, only have LNE, the pump is switched from the wiring diagnostic centre (or in a mess of wires and chop blocks behind the programmer) and switched by the 2 or 3 port valve. Modern boilers tend to have switched live out for the pump over-run so if you know there is chance it is going to be replaced (as sounds likely) in the future, I'd wire it in 5 core back to the wiring unit/programmer.