29 | P a g e
• By removing PWM cable at the pump to allow the 230v cable to power the pump at full speed. To
do this, ensure safe electrical isolation and then use a 4mm electrical screwdriver to push down the
clip below the PWM connector and gently pull the connector out. Re-establish power to the boiler
and the pump should run at full speed.
7. Confirm 230v from the PCB connector CN2, pins 5&6. If no voltage, replace PCB.
8. Check 230v supplied from the PCB to the pump connector. If voltage at pump connector, replace pump.
9. If no voltage at pump connector, use a multimeter to check the wiring harness for continuity from the PCB
via connector CN2, pins 5&6, whilst checking connectors are tight and free from damage or corrosion.
Replace as required.
10. If 230v side ok, check the pump PWM via the 3-wire cable connection to the pump on PCB connector CN9
pin 1&2:
• with the pump off the voltage is +/- 5VDC.
• 39% load the voltage is +/- 3VDC.
• 61% load the voltage is +/- 1.9VDC.
• 100% load the voltage is +/- 0.24VDC.
11. If the above voltages are correct, and the pump does not operate, replace the pump.
12. If the voltages are incorrect, replace the PCB.
13. Check expansion vessel pressure is set correctly as per the manufacturer’s instructions.
14. Check expansion vessel flexi hose is correctly connected with no kinks or blockages.
15. Check the boiler for any blockages or restrictions.
16. After checking all the above points, switch off the power and back on again, allow the boiler to run
automatically through the automatic venting program.
17. If the fault persists, replace the PCB.
141 Description: no flow detected (Regular boiler only).
.
Cause: The flow switch has an open circuit after 5 seconds of operation; 7 l/m +/-10% flow is required to make the
circuit.
A good flowing system will deliver around 20 L/min.
1. Check if happening on CH or HW, or both, and/or on pump over run to help diagnosis.
2. Check the pump is wired directly into the boiler’s green connector.
• If wired externally to the boiler, the pump overrun will not function. Re-wire as required.
3. Check the pump is of suitable size for the system and boiler resistance (index circuit).
4. Check pump type – i.e., is it a modulating pump. This may affect the operation.
5. Check pump speed.
• If older pump, it may have weakened. Check the pump by removing the bleed screw and stopping
the impeller with a screwdriver.
• Check the resistance of the pump which should be approximately 150 Ohms.
• Replace pump as required.
6. Check bypass is of suitable size to function correctly on pump overrun.
7. Check system configuration of open vent and cold feed pipework is correct.
8. Check all isolation valves and TRV’s are open, and filters not blocked.
9. Check for air in the system, vent air if required.
10. If system full of air, temporarily link out flow switch and allow pump to help clear air.
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