Vokera 24 DHW Problem – A real challenge

[Kal]

I am gas safe registered and have a problem with a Linea 24 which has left me stumped, even Vokera technical can’t seem to help on this one.
The Linea 24, provides heating well but only provides luke warm water – The display stops at 38 degrees. When DHW is selected it fires and the gas valve modulates down to 5 mbar straight away. I have read the other posts and have stripped the boiler down but have not managed to rectify the fault.

Here’s the history:
Main heat exchanger was replaced in December as this had a small crack and was leaking. 2 weeks later the DHW fault occurred.
• DHW thermister and main thermister checked, but then replaced to avoid doubt on the advice of Vokera – still no change
• Plate Heat Exchanger tested – Upon closure of cold inlet isolation valve only read 65 on the display, however this was replaced to avoid doubt – Still no change.
• Diverter head checked, Heating Flow/ Return Pipes do not get hot, so not flowing round heating system, motor retracts properly.
• Diverter spindle checked, cleaned lubricated and replaced – Still no change.
• Non return valve checked, cleaned - Still no change.
• Bypass checked, cleaned, cleaned - Still no change.
• Mesh filter cleaned - Still no change.
• DHW flow restrictor checked, cleaned and replaced – Still no change.
• Spindle on PCB checked to ensure that the dial is functioning correctly and this is fine.

I have tested the hot water with a by holding a thermister externally on the DHW thermister connection and the boiler then maintains full flame (10mbar), so the PCB/potentiometer are fine, but when plugged back in the thermister in situ, it modulates down and stays at low flame.

I have stripped the boiler down and cleaned all areas that I think could be causing a restriction, but am truly stumped now. The boiler did have some dirt in it, but I have seen worse and most of this has been cleaned up now. I must be missing something. I would appreciate any advise on this tricky fault.

Thanks,
Kal

 

[nickso]

wiring loom? had this twice on lineas. went through all the usual and it turned out to be a faulty loom to either thermistor.

i know you said it was a 24 but if by any chance you have the model wrong any of the 7 series models use an analogue APS which will cut the burner pressure down if the venturi are even close to being blocked. remove the entire assembly to check.

 

[Agile]

Trade questions are better asked in the Combustion Chamber section of this site.

There we can give you full advice.

Tony

 

[Kal]

Thanks,

I suspected the venturi, but the boiler ramps up to full flame on heating and also when I hold a spare thermister to the connection externally. I just cant understand why it wont do it when i reconnect to the thermister in situ.

Tony - how do i get to the combustion chamber section?

Thanks,

 

[Agile]

Email name, address, gas reg number AND licence number on your card to [email protected]

 

[Kal]

Thanks Tony,

I have now done that, so will hopefully get access details soon.

I also spoke to Vokera technical again and was advised that is most likely to be the PCB. The support person told me that the main PCB is probably faulty only permitting a maximum to 38 degrees, modulating down straight away. When I asked why it ramps up to full flame when I plug in a thermistor externally, he stated that the sensor was still trying to get to 38 dgrees, but as the thermister is external it doesnt know it yet and so does not modulate down. Seems a reasonable explanation, I asked if there was any way of testing this on the board, but did not get an answer.

Before I go out and purchase a new main board has anyone else had this sort of problem with the linea resulting in a main board fault.

This is more about the challenge now rather than closing the job.

Thanks,

Kal

 

[DP]

Kal is boiler functioning OK for CH?

 

[Kal]

Yes CH is perfect.

 

[DP]

Kal have you checked the burner pressure? 38 degrees C is the temperature of hot water NOT primary water temperature.

Have you checked what the cold water temperature is? If it is 3 degrees, then 38 is all you will get at 9.5 l flow rate. If the gas line is undersized, you will not get 35 degrees temperature rise for hot water delivery

 

[Kal]

Thanks DP,

Yes I have checked the burner pressure, when you demand hot water the burner ignites to full flame and then modulates down to 2-3mbar straight away. I have also checked the incoming supply and i'm not getting a proper rise. I am starting to think that the vokera technical support asistant is right and that the control board is only permitting a maximum of 2-3 mbar on DHW.

Just wondered if someone else has had a similar experience.

 

[Agile]

I would love to try to help you as it sounds an interesting fault.

But until its posted in the CC, I would not be able to ask you to do any gas related tests for example.

In any case as a matter of principle I think all trade questions should be asked there anyway.

Tony

 

[weargas]

i've had this Kal. Was advised by Vokera tech to change ignition electrode to a different one at the same time as changing the pcb. Give them a ring again and quiz them about the electrode prob. They couldn't tell me why just said "change it".

 

[DP]

Weargas, would a defective electode not give problematic CH operation too? OP says CH operation is perfect. But then again, CH operation is at 75% power for first quarter hour, and also if burner is downrated, poor CH operation would not be easily seen. HW highlights malfunctions PDQ.

 

[Kal]

Thanks to you all,

I have ordered a new PCB and will go back this week. I'll ring vokera today and ask them if there is a problem with the electrode.

Tony - I did email admin like you suggested, with my registration details but have not received any response yet. does it take a while, or is there something else I can do to speed up the process, as i'd quite like to be a part of the trade forum.

Thanks,

Kal

 

[Agile]

It usually only takes 1-3 days but unfortunately it seems only the site owner does it and if he is sick, snowed in or under then it can take longer or as seems to have happened to overlook it altogether.

Furthermore, it seems that if you dont give ALL you details then its just ignored without any contact back to you.

I sugest you recheck that ALL the details were sent and resend them.

Sorry that I cannot offer any better resolution.

Tony