Why is HIU service important?

HIU is an expensive unit, and with a regular servicing, any problems with the unit can be identified and addressed before any major damage occurs. This ensures that when winter comes and the heating is switched on, there are no surprises.

Serviced HIUs run efficiently, which saves energy and keeps bills to a minimum.

Most common faults with HIUs are leaking joints or leaking internal parts. Sometimes, leaks are not visible from the outside until the HIU cover is removed. Some small leaks can go unnoticed for years due to the heat inside the HIU. Minor leaks tend to stop while the unit is in use and the heat expansion in the metal closes up the source of the leak. After HIU usage stops, the unit cools down and leaks reoccur. This can easily be repaired by replacing the fibre washers on the leaking joints or replacing component parts after they are identified by a servicing engineer.

HIU leaks mostly happen because of joints that are loose, or fibre washers deteriorating in parts or pipe joints. Pipes or components might have been installed at incorrect angles that then create leaks over time.

Another very important cause of leaks is water quality. There are two instances:

1) The mains cold water that runs through the HIU gets heated and comes out of the mixer tap. If you are in a hard water area, scaling can block HIU components and create leaks.

2) The (heating) water that circulates through the radiators into the HIU to be heated and circulates back to the radiators. This water is on a separate circuit and does not mix with the hot water that comes out of the taps. Heating water should be treated and dosed with an inhibitor chemical to prevent dirt, rust and sludge inside HIUs, pipes and radiators, which will in turn prevent leaks in the HIU system.

One other HIU fault that is very common is incorrect settings on the heating control valves and hot water control valves inside the unit. Firstly, a property’s correct heating strategy should be identified. For example: is the property’s heat source underfloor heating or radiators? This will dictate the temperature set up for the HIU heating control valve. The heating pump speed should be set to match the heating system; while the hot water regulating valve is to be set to deliver at least 45°C within 45 seconds of turning the kitchen tap on at full flow rate. The correct HIU settings will enable the unit to work at optimum efficiency and safety.


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