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- 4 Oct 2005
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Greetings all, haven't been here for a long time 
A customer had a problem with DHW going hot-cold-hot, etc. Also complained of F23 fault code regularly. The fault log confirmed this.
After descaling the DHW H/E I found the gas valve was not modulating properly, just oscillating between full rate and low/off. Equally the CH wouldn't ramp-up, staying at minimum gas rate. It's a rented house so (unsurprisingly) the cover was missing from the modureg adjusters. Don't landlords just love to poke & prod
I took advice from Vaillant and, when they eventually answered the phone, they were very helpful, advising me to check the voltage across the modureg terminals (expecting about 15vdc when on P1/P2 test mode). This wasn't the case, only 0.8vdc connected, but 24vdc+ open circuit. Was advised to change the PCB, but decided to avoid this until absolutely necessary as DHW duty certainly drove the modureg to full rate. Rang back....waited....waited...told how important my call was...waited...got a second opinion - advised to change the flow & return temp sensors. As they are relatively cheap I did just that, and BINGO, boiler back to life, modulating properly, DHW temp stable.
Of interest:-
1. Both old sensors tested in situ before removal @about 1kohm each @50C, remeasured when cold @about 3kohm each, the same as the new ones!
2. P1/P2 worked properly after fitting, not before.
3. Don't trust the inbuilt diagnostic code D37, it infers modureg current rather than measuring it - so it's the same open or closed circuit
4. Don't follow advice given over the phone blindly, it's an opinion, just like the ones expressed here, and can be wrong.
So to the question...has anyone else had the same experience, and what does F23 signify - my manual doesn't list it, and Vaillant website seems to be dead on the tech help side.
Regards..MM
A customer had a problem with DHW going hot-cold-hot, etc. Also complained of F23 fault code regularly. The fault log confirmed this.
After descaling the DHW H/E I found the gas valve was not modulating properly, just oscillating between full rate and low/off. Equally the CH wouldn't ramp-up, staying at minimum gas rate. It's a rented house so (unsurprisingly) the cover was missing from the modureg adjusters. Don't landlords just love to poke & prod
I took advice from Vaillant and, when they eventually answered the phone, they were very helpful, advising me to check the voltage across the modureg terminals (expecting about 15vdc when on P1/P2 test mode). This wasn't the case, only 0.8vdc connected, but 24vdc+ open circuit. Was advised to change the PCB, but decided to avoid this until absolutely necessary as DHW duty certainly drove the modureg to full rate. Rang back....waited....waited...told how important my call was...waited...got a second opinion - advised to change the flow & return temp sensors. As they are relatively cheap I did just that, and BINGO, boiler back to life, modulating properly, DHW temp stable.
Of interest:-
1. Both old sensors tested in situ before removal @about 1kohm each @50C, remeasured when cold @about 3kohm each, the same as the new ones!
2. P1/P2 worked properly after fitting, not before.
3. Don't trust the inbuilt diagnostic code D37, it infers modureg current rather than measuring it - so it's the same open or closed circuit
4. Don't follow advice given over the phone blindly, it's an opinion, just like the ones expressed here, and can be wrong.
So to the question...has anyone else had the same experience, and what does F23 signify - my manual doesn't list it, and Vaillant website seems to be dead on the tech help side.
Regards..MM
