(Vaillant preferred heat pump installer partner)


Normally, I install heat pumps in new build developments where the heat pump, with integrated auxiliary heater, is the only heat source for space heating and domestic hot water.

At this particular installation the customer wanted to combine his existing two year old gas boiler as backup to the heat pump. The customer also wanted to maintain the flexibility so that they could upgrade the system further in a few years to include a solar hot water. To achieve this complex system I decided to utilise a Vaillant multi-storage cylinder as a thermal store.

This mulit-storage cylinder has a capacity of 500 litres, which is enough to keep the heat pump running for long periods, maximising the efficiency of the system. The multi-storage cylinder has enough tapings to connect the heat pump, the gas boiler and the flow and return for the underfloor heating system. An additional option to add a solar heat exchanger is provided, which the customer will use in a future upgrade. The multi-storage cylinder has an integrated heat exchanger to produce domestic hot water.

Between the heat pump and the gas boiler I installed an additional communication unit so that the heat pump and the gas boiler could work together in an efficient manner. The heat pump runs under normal conditions and only when higher temperatures or larger outputs are needed will the boiler operate.

After I filled up the heating system, I insulated all pipework to minimise energy loss. The pipework in the heating circuit was insulated with a thermal insulation against energy loss, whilst the pipework in the ground loop circuit within the garage was insulated with a water proof insulation to avoid condensation forming on the pipes.


What we learnt: Multi-energy source heating systems, including a heat pump, are complicated to set up and control. In existing houses such a solution has to be designed to provide the different temperatures and heating outputs required by the various parts of the system. Some alterations to the existing system, such as the removal of redundant hot water storage cylinder or system by-passes, may be required.