Rayburn Back Boiler Cooker Addition to Existing Pellet Boiler System

Existing system

It is a post RHI system with a pellet boiler working on an underfloor heating system. Hot water is being produced in indirect cylinders.


The existing system is fairly complicated and works good, we didn’t want to modify it too much. We just used two free connection of the buffer tank. Through these we heat the buffer tank similar to the pellet boiler, and the existing heating system remained unmodified. The only modification was the installation of a relay in the pellet boiler which made it possible to block the operation of the pellet boiler if there is enough heat from the Rayburn cooker.


The existing system is pressurised, but the Rayburn must be installed open vented. We made a small open vented system only for the Rayburn and connected it to the buffer tank through a plate heat exchanger.
The heat exchanger
The heat exchanger with the primary and secondary pump of the Rayburn, and the controller.


There is not any ready made controller for this specific system layout. This is why we used our universal controller.

Mixing valve

A VTC511 mixing valve has been installed to keep the heat exchanger and so the Rayburn cooker hot during operation to prevent it from corrosion.


Normally filters are not installed into system with Rayburn stoves. This filter is not to protect the stove but the relatively sensitive plate heat exchanger.


Buffer tank
Buffer tank
Rayburn cooker
Rayburn cooker

Initial problems

The original plan was not to modify the existing heating control system, but at the end we had to.
The problem was that even without the operation of the pellet boiler the buffer tank became overheated just by the Rayburn stove.
To eliminate this we used a free output of the controller. If the temperature of the buffer tank or the stove rises above a certain level, we override a room thermostat of a heating zone and start to heat that zone.

MCS certificated
Home Improvement Protection
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