Heating only getting to 42deg

[The831Bunny]

So to recap, you have no thermostat wired to T3 & T4 (its linked out with a wire link), There is NO time clock plugged in your boiler fascia, and you just have a LNE supply wired to the PCB?

 

[mark paterson]

Yes that is the case. I havnt a clue now. Thanks for your help by the way.

 

[picasso]

Now that d5 is reading 85c (and you havent turned the dial back down) is the boiler still stopping at 42c ?

 

[The831Bunny]

From the end of a computer keyboard (or iPhone in my case) its always difficult to not put ideas into people's heads why I'm asking these questions, but given what you have said it has to be a PCB fault. As you have changed this, all things equal, it must be something else.

Check the white wire that is screwed to the front of the chassis is clean tight and sound. Check the polarity LNE wise is correct. Check for any fault codes in the history (- & i together), especially F.20-24 and F.64 codes. Also check nothing is connected to any other terminals on the PCB (7,8,9 especially). Also check you have a maximum of 5VAC on the Neutral connection measured to earth.

Then I'm afraid you are into using the services of somebody who is Gas Safe registered and conversant in Vaillants to check components in the combustion chamber. It's a possibility that the display PCB is faulty, but that's a very rare occurrence, but not impossible. Can't remember the last time I changed one for temperature related problems, maybe 10 years or more!

 

[Agile]

Also check you have a maximum of 5VAC on the Neutral connection measured to earth.

Just in case you get confused with that too, he means measure it and make sure it is LESS than 5 v AC.

 

[mark paterson]

I have done all of the above and evrything looks okay. I have an F24 in the fault history f28-29. I cant find what f24 is though?

 

[Agile]

On those boilers whose PCB supports it, F24 means there is too small a temperature difference between the two heat sensors.

That can be a sticking or blocked pump, other blockages, out of tolerance sensors. Even air in the heat exchanger.

If you have kept on draining and refilling you may have turned on the boiler without enough flow rate and caused a sensor to overheat which can alter its characteristics.

Tony