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12 Fault Finding
12.3 Poor Hot Water Checklist – Always check the basics before changing parts!
Burner If heat energy input is incorrect: Check nozzle is correct size.
heat energy output will be Incorrect. Check oil pump pressure is correct.
Poor heat input = poor hot water! Check combustion is correctly set.
DHW Pump Plate heat exchanger requires water Check pump speed setting: it must be maximum.
circulation from primary store to operate Check pump valves are fully open.
Thermistors DHW “Store“ and CH “Flow“ thermistors Check both are fully inserted in their pockets.
must detect temperatures correctly
Water Flow Rate Excessive flow rate exceeds heat input Check flow rate at tap.
at Hot Tap from burner Combi 21e – 12 ltrs/min maximum
Excessive flow rate=poor hot water! Combi 26e – 15 ltrs/min maximum
Combi 36e – 18 ltrs/min maximum
Water Pressure Excessive pressure has a major Check standing and operating water pressure.
influence on flow rate. 2 bar minimum standing pressure required
8 bar maximum standing pressure.
If greater than 8 bar: fit a pressure reducing valve on
the cold supply to the boiler.
1 bar minimum dynamic pressure required.
Water Condition Scale forming in the plate heat exchanger Check for scale in plate heat exchanger.
= poor heat transfer in plate = poor hot Replace plate heat exchanger if necessary.
water temperature. In hard water areas some form of anti-scale device or
water softener MUST BE FITTED.
NOTE: Faults due to hard water scaling are not
covered by the Grant Product guarantee.
Thermostatic Must be correctly set to provide Check if blending valve is scaled up (see ‘Water
Blending Valve Optimum hot water. Condition’ section above).
Clean or replace as necessary.
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