40
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.
