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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.
201 Description: T3 Hot water sensor defective.
Cause: The values of the T3 hot water sensor outside specifications (iC & iCE boilers only).
1. Check full T1 wiring harness and connectors for signs of damage, corrosion, or loose contact.
2. Use a multimeter to check if T3 sensor resistances are in line with the return temperatures and per the table
on page 67.
• The return temperature can be identified using the customer information menu.
• The resistances can be taken at the connector at the PCB CN12, pins 1&2. This checks the
wiring harness continuity at same time. Disconnect the connector from PCB 1
st
to ensure no
additional resistances are given through the PCB.
• If the readings are incorrect, disconnect the wiring harness from the sensor and check the
sensor readings without the harness to prove if the sensor or harness is the fault.
Note thermistors may need cleaned and not always replaced.
3. If 201 appears on a non-combi boiler, check parameter 2.2.8 and change the setting if required. Restart the
boiler from the power supply.
4. If changing the parameter does not work, carry out a factory reset on the PCB using parameter 2.8.0. If this
does not work, replace the PCB.
203 Description: T3 Hot water sensor defective.
Cause: The values of T3 boiler sensor out of specification (iS & iR boilers only).
1. Check the Hot water priority DHW NTC sensor is connected to the boiler.
2. Check the boiler sensor wires for loose contacts and breaks.
3. If the cable has been extended, check the wires at the junction box/block connector.
4. Check if the sensor is installed correctly.
5. Check the resistance of the sensor per the table on page 67 from the yellow DHW connector at the boiler
and replace if required.
6. If after changing the sensor, the fault does not clear, carry out a factory reset on the PCB using parameter
2.8.0. If this does not work, replace the PCB.
7. If no sensor is fitted to the boiler, check parameter 2.2.8 and change the setting if required. Restart the
boiler from the power supply.
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