John asks this question about an unusual domestic dual-boiler installation. It has been answered by Horstmann Controls (Theme – Electrical Heating Ventilation and Control):
This Q & A is one of thousands posted in our Technical Expertise area, and answered on a daily basis by our Voltimum Experts.
Question: Because of a plumbing issue, we now have to wire a second boiler alongside another in a reasonably sized house.
This house has two water cylinders and two zone valves for heating, controlled by two remote thermostats.
The plumber is of the idea he will just connecting on to the original. I think, however, that some re-piping is required, so that one boiler operates one valve and the other runs other zones. Am I right?
Answer: Commenting on this is difficult without further detail on the existing system and what the real purpose is behind the installation of a second boiler, which is unusual in a domestic installation.
Normally the thermostat, when calling for heat, provides a switched supply to the motorised valve, which when it opens, provides a switched supply to the boiler.
Therefore, if the additional boiler is intended to supply a different heating zone, one would expect the control circuitry and the relevant parts of the heating pipework to be separate.
If the intent is just to increase the available heat output for the system as a whole, then linking the two boilers could make sense, but the plumbing implications of that is not our area of expertise.
In either case, one should follow the advice of a suitably qualified heating engineer and if the proposal from the current contractor doesn't seem to make sense, it would be worth seeking a second opinion.
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