Master/slave control of two boilers on one system

morrismoaner · 6 Nov 2012

Hi

I am trying to source a module that will give control of an S plan system connected to two boilers. The master boiler is fueled by waste oil but if this boiler fails I want to automatically switch over to my convential boiler to continue to provide heating and hot water to my home. Has anyone ever used or seen a unit that will give this kind of control?

I was thinking of maybe using a pipe thermostat, relay and timer so that the switch wire from the S plan will power the oil boiler but if the stat does not detect heat after x amount of time then the relay will switch power to the conventional boiler.

Just a forethought to start with, would very much appreciate any comments, ideas or experience of similar systems

Many thanks

stem · 7 Nov 2012

Unfortunately it is not quite that simple, if you intend to connect two heating sources together you need to use a Neutraliser. An example can be found here. There is a link to the wiring diagram. Other makes are available

dcawkwell · 7 Nov 2012

You can do it with a pipe thermostat check the warmflow website.
They give an example of a boiler cascade setup.

morrismoaner · 7 Nov 2012

Many thanks to you both for your replies. The cascade system is very similar to my requirements.

stem · 8 Nov 2012

When you said "conventional boiler" I thought you were referring to a solid fuel boiler. They have different requirements as they don't have thermostatic control that turns the heat off like gas / oil boilers.

Norcon · 8 Nov 2012

Some fag packet thoughts very quickly.
A - Boilers connected in parallel with separate pumps.
B - On delay relay energising pipe stat.
C - Second relay de-energising waste oil boiler and pump.
D - Third relay energising gas boiler and pump via pipe stat "demand" contact.
E - Termovar or similar valve fitted to return of waste oil boiler.

mysteryman · 8 Nov 2012

Does the first boiler have an external fault signal capability? If so, it could be used to bring the second boiler on.

morrismoaner · 8 Nov 2012

Does the first boiler have an external fault signal capability? If so, it could be used to bring the second boiler on

Thats a great idea, the lockout neon could energise a relay to drive a motorised valve that will switch the second boiler on. I'm thinking of also adding a selector switch to choose which boiler can be manually switched by the S plan controls.

Brilliant ideas guys, keep em coming. I intend to post what I have installed when it has been tried and tested for future reference to all.

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Master/slave control of two boilers on one system

mysteryman

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