10 | P a g e
128 Description: Ionisation current too low.
Cause: Ionisation level too low at max fan speed/RPM.
1. Check condensate pipe is clear of blockages and is running freely. Clear as required.
2. Check 230v at gas valve, connections 1 & 3.
a. If the voltage is correct, move to step 3.
b. If there is no voltage at the gas valve, check the PCB is sending 230v to the gas valve from connector
X12, pins 1 & 2. Replace PCB if there is no voltage.
c. If voltage is supplied from the PCB, check the condition of the wiring harness and connectors. Use a
multimeter to confirm continuity throughout the cables. Replace harness if faulty.
3. Check the working pressure at the P1 test point of the gas valve with all gas appliances in the house fully on.
The WP must be no less than 4mb under that of the WP at the gas meter for NG or 2.5mb for LPG.
a. If WP at the meter is under 19mb call National grid or local network to investigate the issue.
b. If under pressure at the boiler, investigate secondary isolation valves, pipe sizing or shale/debris, etc.
in gas pipe.
4. If the working pressure is correct, check the following:
5. Check ionisation current is between 0.8μA & 4μA using the A menu & A8.
6. If ionisation current is ok, proceed to step 7.
a. If ionisation current is too low, check earthing in house with an earth loop impedance tester.
b. If earthing in the property is ok, move to step 8.
7. Check 230v at the ignition transformer, connections 1 & 2 (black wires).
a. If the voltage is correct, move to step 8.
b. If voltage is incorrect at the ignition transformer, check the PCB is sending 230v to the ignition
transformer from connector X12, pins 3 & 4. Replace PCB if there is no voltage.
c. If voltage is supplied from the PCB, check the condition of the wiring harness and connectors. Use a
multimeter to confirm continuity throughout the cables. Replace harness if faulty.
8. Check voltage from the transformer to the electrodes. Using a multimeter, check for between 60-100 volts
AC between both outlet connections of the transformer to an earth connection (the 100 volts should be on
initial startup and then settle to approx. 60V). If voltage incorrect replace transformer or if voltage correct,
proceed to step 9.
9. Check the spark gap and condition of the electrodes, including the ionisation electrode. The spark electrodes
should have a 3 – 4mm spark gap and be clean. Adjust spark gap and clean electrodes with a fine sandpaper
if required. If still fails after cleaning and adjustment or is worn out, replace electrodes.
10. Check if the CO/CO2 values are correct.
11. Check the condition of the burner for any debris or cracks, clean or replace as required.
12. Check the non-return valve in the fan is operating correctly, replace as required.
13. Check heat exchanger flue ways are clear of debris. Clean with a soft brush and vacuum cleaner as required.
14. Check boiler for recirculation of products of combustion and repair as required.
15. Check flue length and configuration is correct as per the manufacturer’s instructions.
16. Check flue for breaks and carryout O2 checks to confirm no spillage of products of combustion.
17. Check boiler is set to the correct gas type using the P menu & P5, whilst ensuring LPG boilers have the
correct restrictor fitted at the fan.
18. If all the above have been checked and the fault remains, replace the PCB.
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