Vaillant Ecomax VUW 236H Boiler Fault Codes

F0/F20

(alternating display) Interruption to NTC flow sensor 'T0'*

1. Loose wire/poor connections to NTC 'T0' - Repair as necessary.

2. Faulty component - Replace NTC 'T0' (Section 7.8)

F1/F20

(alternating display) Interruption to NTC flow sensor 'T1'*

1. Loose wire/poor connections to NTC 'T1' - Repair as necessary.

2. Faulty component - Replace NTC 'T1' (Section 7.8)

F2/F23

(alternating display) Interruption to NTC heat exchanger sensor 'T2'*

1. Loose wire/poor connections to NTC 'T2' - Repair as necessary.

2. Faulty component - Replace NTC 'T2' (Section 7.8)

F10/F20

(alternating display) Short circuit to NTC flow sensor 'T0'*

1. NTC 'T0' connection wire short circuit to earth

- Repair as necessary.

2. Faulty component - Replace NTC 'T0' (Section 7.8)

F11/F20

(alternating display) Short circuit to NTC flow sensor 'T1'*

1. NTC 'T1' connection wire short circuit to earth

- Repair as necessary.

2. Faulty component - Replace NTC 'T1' (Section 7.8)

F12/F23

(alternating display) Short circuit to NTC flow sensor 'T2'*

1. NTC 'T1' connection wire short circuit to earth

- Repair as necessary.

2. Faulty component - Replace NTC 'T2' (Section 7.8)

F20

Shutdown by overheat thermostat 

F21/F25/F48/F50

(alternating display)

Faulty Fuse

4A Fuse F4 defective

- Replace fuse with spare provided

F21 

Flame Failure Fault

Enter diagnostic mode (see Section 8.1), select 'd.66' and press the right button.

if d.66 = 0, power supply to boiler has been interrupted since fault occured - proceed as for d.66 = 2

if d.66 = 1, fault occurred before ignition, CPU circuit board is defective. Replace (see Section 7.22.4)

if d.66 = 2, fault occurred during ignition.Possible causes: gas supply disturbed or air in the supply network. Check that the gas supply is turned on and that it has been correctly purged (see Section 5.2). Press the 'Reset' button. Boiler will attempt to re-light. Is a spark visible at the ignition electrodes?

if no:-

Turn the central heating control to the 'hot water only' position and push the red 'reset' button. Enter diagnostic mode, select d32 and push the right button. Turn the central heating control back to the 'heating and hot water' position to operate the appliance for heating. The boiler will attempt to relight. Check the ignition transformer operation using diagnostic code d.32 during the ignition cycle (approx 10 seconds).

if d32 = 1, (during ignition cycle), check ignition electrode, the ignition lead connections to transformer and electrode, if all o.k. replace ignition transformer (see section 7.13).

if d32 = 0, (during ignition cycle), CPU circuit board is defective, replace (see section 7.22.4).

if yes:-

(1) No flame visible before boiler shuts off: gas valve or gas valve connections defective, repair or replace as necessary (see Section 7.9)

(2) Flame is visible before boiler shuts off: Turn the central heating control to the 'hot water only' position and push the red 'reset' button. Enter diagnostic mode, select d21 and push the right button. Turn the central heating control back to the 'heating and hot water' position to operate the appliance for heating. The boiler will attempt to relight. Check the flame sensing system using diagnostic code d.21 during the ignition cycle (approx 10 seconds).

if d21 = 0, Check flame monitoring electrode and lead for damage / correct connection. Repair or replace as necessary.

if d21 = 1, CPU circuit board is defective. Replace (see Section 7.22.4)

if d66 = 3, fault occurred during operation. Check availability of adequate gas supply (see section 5.8). if o.k. check for flue gas recirculation caused by damage to burner or condensate sump seals, check condensate sump draw handle correctly fitted. Repair or replace as necessary.

F22 or F23 

Lack of water in system or poor/no water circulation

1. System water pressure too low - Refill and repressurise the boiler to 1.2 bar (see Section 5.4).

2. Circulating pump not operating - Enter diagnostic mode (see Section 8.1), select 'd.10' and press the right button. Operate the boiler.

if d10 = 1 check the electrical connections to pump and that the pump is not seized. Repair/replace the pump as necessary (see Section 7.14).

if d10 = 0 replace the CPU circuit board (see Section 7.22.4).

F24 

NTC temperature comparison error 

NTC 'T0'* and 'T1'* not giving comparable signals - Check NTC 'T0' and 'T1' connecting leads for continuity and repair as necessary.

If fault still exists, replace NTC 'T0' and 'T1'. * For location of NTC sensors refer to Section 2.4 Function diagram

F25 

Faulty Fuse

F30 or F32 or F33

Lack of air flow through appliance

1. Air/flue duct obstructed

- check terminal is clear of obstruction, and the flue is correctly assembled with flue seals and air duct clamps.

2. Condensate drain obstructed - check condensate discharge pipe not obstructed.

3. Faulty fan - check fan performance using diagnostic codes 'd.33' and 'd.34'. Enter diagnostic mode, select 'd.33' and press the right button. Operate the boiler. Note the reading obtained.

Now select 'd.34' and press the right button. Compare the reading achieved on 'd.33'(the required fan speed) with the reading obtained on 'd.34' (the actual fan speed). If the actual fan speed reading is more than 20 below the required fan speed check the connections to the fan motor. If electrical connections are satisfactory replace the fan (see Section 7.2).

F31 or F34

Air pressure sensor fault

1. Initially check both air/flue duct and condensate discharge are free of obstruction.

- Remedy as necessary.

2. Air pressure sensor connections not correctly located in gas valve. - Relocate sensor as necessary, check conection lead.

3. Faulty component - - Replace air pressure sensor (see Section 7.3)