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The heating system should be installed by a competent installer in accordance
with the recommendations laid down by the building services compliance guide,
OFTEC and sound engineering practice.
In order to comply with building regulations, the boiler passport and or
OFTEC forms CD10 for installations and CD11 for commissioning should be
left with the customer. Alternatively the installation can be inspected and
approved by a building control officer.
4.3 Combi General Requirements
The boiler will have a DHW priority when both domestic hot water (DHW) and
central heating (CH) are selected. So if the flow switch is closed or the heat store
has not been satisfied the entire output of the boiler is directed to DHW before the
boiler will switch over to CH. When fully cold it can take up to 20 minutes for the
heat store of a 90,000 Btu/h combi to be satisfied, and slightly longer for a 70,000
Btu/h combi.
After a draw-off of 120L at 24L/min, with an average temperature rise of 32ºC, the
thermal store of a 90,000 Btu/h combi has a recovery time of approximately 7
minutes. A 70,000 Btu/h combi will take slightly longer to recover.
Note: If HW has not been selected no hot water can be produced even if the heat
store is up to temperature.
4.3.1 Pump Overrun
Where there is a build up of excess heat in the boiler primary heat exchanger and
the central heating has not been selected then the pump overrun thermostat will
operate. The excess heat will then be pumped into the heat store. Once the
temperature has fallen in the boiler and the pump overrun stat is satisfied, then
the hot water pump will stop.
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