51 | P a g e
• 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.
11. Check flow and return pipes not reversed.
12. Check system for blockages and remove.
13. Remove flow switch and check continuity when making and breaking the switch manually. Replace flow
switch as required.
14. Use a multimeter to check the wiring harness to the flow switch for continuity from PCB connector CN12,
pins 9 & 10, whilst checking connectors are tight and free from damage or corrosion. Replace harness as
required.
15. Loosening the flow switch and turn so arrow on the end points to 11 or 1 o’clock can allow better movement
of the paddle to detect the flow.
142 Description: Pump feedback open short circuit.
Cause: The pump PWM signal has been interrupted.
1. Where possible, use the customer information menu to check the pump PWM % and the pump flow rate.
2. Use the pump LEDs on page 66 to assist with diagnosis.
3. Check the operation and voltage of the pump with a demand.
You can force the pump 'on' via 2 methods:
• Preferred and safest method by using manual settings in parameter menu 2. Set parameter 2.6.0 to
1 = Manual mode On, and 2.6.1 to 1 pump control 'On'. Please note change 2.6.0 to 0 manual mode
'off' after this test.
or
• 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.
4. If the pump does not run, check 230v supplied from the PCB to the pump connector.
5. If voltage at pump connector, replace pump.
6. If no voltage at pump connector, check wiring harness and connectors for damage, corrosion, and loose
connections.
• Confirm continuity with a multimeter and replace harness if required.
7. Confirm 230v from the PCB via connector CN2, pins 5&6. If no voltage, replace PCB.
8. If 230v side ok, check the pump PWM via the 3-wire cable connection on the pump and pins 1 & 2 on the
PCB connector CN9:
• 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.
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