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4.0 Servicing
4.1 Draining down
CAUTION: Servicing should only be carried out by a Herz approved service engineer.
CAUTION: The district heating side of the HIU can be operated with high pressure and temperature systems.
Please apply extreme caution and wear the appropriate safety equipment (PPE) when working on suspected
leaks.
Draining down the primary
Close the primary flow and return ball valves and open the manual air vents to release the pressure.
Open the drain valves on the primary flow and return ball valves carefully and drain into a suitable container.
Draining down the domestic hot water
Close the mains cold water inlet ball valve and open a hot tap.
Open the manual air vent positioned above the pressure temperature control valve.
Open the drain valve on the mains cold water inlet ball valve carefully and drain into a suitable container.
If the HIU is installed for top entry pipework with the ball valves at the top of the unit, the draining functions
will be carried out with the two drain valves situated at the bottom of the unit and the drain valves fitted to
the ball valves will be used as air vents.
4.2 Component servicing
In hard water areas lime-scale can build up in the system. Depending on the hardness of the water, the unit
should be de-scaled by a professional every one to two years. If lime-scale build up in the system is excessive
some of the valves could be damaged, these should be replaced immediately to ensure reliable operation of the
heating system.
Do not clean the unit with scouring or harsh cleaning agents. Wipe it down with a damp cloth which has been
rinsed in water with a few drops of mild detergent.
Domestic water Heat exchanger
Routine servicing
– Check all connection seals, check all temperatures against the commissioning data and
change the heat exchanger if the DHW temperature is significantly reduced.
Component replacement
– Drain the primary and domestic sides of the unit. Undo all 4 connections and
remove the heat exchanger. Replace the heat exchanger, refit the connection nuts replacing the seals.
Ball valves
Routine servicing
– Operate valves regularly and check all connection seals.
Flow restrictor
Routine servicing
– Located directly underneath the Pressure temperature control valve between the two
union nuts on the cold water feed. Check all connection seals and drain the domestic side of the unit. Undo the
union nut on the cold water feed at the water meter spacing piece, undo the union nut at the double union on
the pipe and remove the pipe, undo the union nut at the PTC valve connection to access the flow restrictor. The
flow restrictor is now accessible inside the connection immediately below the inlet to the pressure temperature
control valve. Remove the flow restrictor noting its flow direction, inspect for damage and debris, clean and refit
into the connection pipe. Reassemble the pipework in reverse making sure that all connections are tightened
correctly.
Component replacement
– Same procedure as above replacing the flow restrictor with a new component.
