s plan with back boiler

Doomed · Jul 2, 2014

I'm quite happy with wiring in an s plan from scratch normally, but this is the first time that I have had to incorporate a back boiler.
As yet the only information I have been given is that I'm doing an s plan with back boiler - wow, thanks boss.
Any clues or advice about what is different to a normal s plan - im going to guess that there is an additional stat for the back boiler, and a means of pumping hot water away from the back boiler if the normal boiler is not active.
Thanks in advance.

davesparks · Jul 2, 2014

Depends on the system but generally there will need to be safety stats/interlocks.
Somewhere for excess heat from the back boiler to go.

Back boilers don't supply heat on bemoans the same way a gas or oil boiler does, they churn out heat non stop and you have to find somewhere to loose the excess otherwise the water will boil and then KABOOM!

Doomed · Jul 2, 2014

After trawling the interweb for more insights I have found that baxi now do a combined back boiler that you will treat as a normal boiler for wiring purposes )perm live and switch live) the rest of it is sorted by the plumber.

Also some older back boilers relied on convection to lose their heat to the cylinder which was then open vented.

More clues would be welcome, but I have a feeling it will be a case of turn up and see what I've got to play with.

Richard Burns · Jul 2, 2014

I would have said that you would need a radiator constantly connected to dump excess heat, often a bathroom or towel rail radiator.
A pipe stat to monitor overheat in the back boiler may be required depending on type.
The rest of the system should be standard.
However this is just my thoughts and turning up and dealing with it may be the best solution!

Perci · Aug 25, 2014

I have wired one of these systems recently and the way theirs worked was it had a switch beside the fire that had to be turned on when the fire was lit. This turned a pump on and allowed the heat to pass in to all the rads and cylinder. This was a crude design as I would have preferred to see the pump automated by a thermostat and a heat store for the excess heat.