Vokera Linea 35HE combi boiler. DHW problem...now failure!

[PUTWADE]

Okay, I am having a bad boiler day. My Boiler is a 3 year old Vokera Linea 35HE. It was fitted to a part existing system ( 3 rads) and was extended (6 rads). I live in the Edinburgh area so Limescale not a problem here. To recap what's happened and what I and the engineers have done:

1 Over the past few months my Vokera Linea 35HE has started running hot then cool/cold with the DHW demand. It has been steadily getting worse.

2 On Saturday, a Heating Engineer replaced the secondary DHW thermistor - the fault appeared to be fixed but it returned in the evening.

3 On Monday; a different engineer (same firm) cleaned muck from the condensate trap - but the fault returned again within the hour.

4 On Tuesday I tested the temperature difference at 40C DHW by turning off the hot tap at 40C and noted the resultant primary temperature displayed which was 60C. (Perhaps indicating not a blocked Heat Exchanger?)

5 On Tuesday evening; yet another engineer (same firm) phoned to say the problem was definately the Printed Circuit Board. I queried if it could be the primary thermistor or Heat Exchanger and he said no chance. I haven't asked him to come out yet as he didn't seem to be interested in what had happened so far or what the symtoms were.

6 Tuesday night, I drained down the system and flushed some clean water through it before re-pressurising adn bleeding rads....This seems to have exasperated the problem, the boiler now does not appear to fire (no flame symbol on the display) although it does heat the water a bit so it must be firing for a short time. It flashes fault code 12 when it is trying to heat then resorts to code 10 (no flame detected) and requests a reset. Occasionaly the final fault code is 52.

7 Wednesday, I replaced the primary NTC thermistor and tried again. Still no joy.

I am now not sure if I've created a new problem or not. The boiler has been re-started/ disconnected from mains/ hold reset button in for 10 seconds etc. I thought perhaps there was air in the pump but it is all automatically released so shouldn't be that.

Any thoughts anyone. DP are you still online?
GW

 

[PUTWADE]

Can anyone help here? I would much appreciate it if so?

 

[gas4you]

Could be the system side of the plate HE blocking.

If it was the domestic side, I would expect it to lock out on overheat.

Just looked up the MI's, I assume you mean you have a 36HE? as they do not seem to list a 35

Code 52 points to a possible issue with the pcb.

 

[nickso]

Code 52 points to a possible issue with the pcb.

better hope not, they are pricey. im dreading mine going.

 

[PUTWADE]

The boiler is 35HE on the Users Instructions and Installation & Servicing Instructions and 35HE on the boiler. However, the downloadable instructions from Vokera only list the boiler as 36HE so I think it's basically exactly the same boiler.
Blocking on System side of the HE would make a bit of sense given part of the CH system was existing and probably had some deposits in it. It looks very tricky to get to the plate HE although a few other posts said a 5 minute job...anybody know or have images of accessing themselves?

The code 52 was the latter code which just started happening more recently. Intitally it was code 10 and 12.

Thanks

 

[PUTWADE]

Just had the problem fixed. The main suspect, the Heat Exchanger was fine (primary and plate) and the thermistors were not the problem. It was the main Printed Circuit Board (thanks Gas4you, code 52=pcb error) that was at fault which a Vokera engineer fixed for a £185 charge.

The initial problem appeared to be with the DHW only running hot then cold but it turns out the central heating system was also making the boiler stop/start and not reaching the high temperatures. This went unnoticed by me, as a symptom, as the radiators appeared warm.