Vokera Linea 24 DHW issue

[Maboza-Ritchy]

Hi
This problem started with the boiler not firing and going out on Fault 01.
The main PCB (board with transformer & relays on it) was replaced albeit some wiring/jumpers on new board had to be change to allow the board to be compatible with the boiler. Boiler installed 1999.
Since then we now have CH & DHW but if you run DHW while having a shower the temp cycles between hot (correct temp) and cool, then back to hot. I've watched the boiler while shower is on and noticed that when the temp guage reaches 51 degrees the burner turns off and when temp drops to 42 degrees the burner fires back up until temp again reaches 51 degrees then off again. The boiler burner cycles like that all the time the DHW is on. Is this normal? We did not have this issue before the board change. Could it be a setting on the board that is causing burner to cycle on/off?

I would have thought that if the water temp was approaching its limit the gas valve would modulate to reduce the flame rather than the flame turning off.

Any advice on this will be greatly appreciated.

 

[Agile]

The boiler will only modulate if the PCB is working properly and if the gas valve is properly set.

If the loose wire on the modulating coil is pulled off when operating, does the flame get small ?

Tony

 

[DP]

Perhaps we SHOULD not be encouraging gas related repairs/ tinkering to end user Mr A!

 

[Agile]

He already seems to have replaced PCBs which I would never advise on this boiler so I dont see merely dissing the mod coil for a moment is very risky for him.

Unfortunately some will spend a fortune replacing parts instead of calling an engineer to correctly diagnose faults.

Tony

 

[Maboza-Ritchy]

DP, Agile,
Thanks for your replies. I've since had a CH engineer look at the problem which has been cured by fitting new plate to plate HE. The engineer showed that the the temp at primary HE was to high causing the burner to switch off when water temp was 52 degrees, output at primary 85+ degrees.

My question to you if I may ask is; on my vintage of boiler, Vokera Linea 24 installed 1999 is, when on DHW should the burner turn on/off to control water temp, ie off when water temp reached 62 degrees and back on when temp drops to 51 degrees or should the gas valve modulate to reduce/increase flame to control temp?

Look for ward to hearing from you.

 

[sandybeach]

As soon as the burner cuts off, close the hot tap and check the temp displayed on the boiler. If the temp is over 80 degrees then your looking at a problem with a choked plate heatex.

 

[Agile]

OK then Maboza, savabona!

The boiler should modulate the gas input down to heat the water from a full flow rate of about 9 litres/min to about 3 li/min at which point if the flow rate reduces any more the burner will have to turn off completely.

Tony