Vokera Linea 28 combi boiler. DHW problem

[RHS]

Some off the posters on here have hit the nail on the head and some are talking cr@p.

You have a blocked domestic heat exchanger (other name is water to water heat exchanger).

One question, have you ever had your CH system cleaned?

More likely NO........you need to clean your CH system to prevent fault coming back in a few months time first of all, second (if you have time) you need to take the heat exchanger off (really easy should take 5 mins) clean it out with a industrial strength drain cleaner I use shift-it works a treat. BUT ONLY PUT IT IN THE CH SIDE NOT THE DHW. leave in for a couple of days wash out and re-fit.

The other way is purchase a new heat exchanger (about £80) and swap out only take about 30 mins.

Don't throw away the old heat exchanger you can still clean it and put it aside as a spare.

 

[davebgas]

Just a tip here for you..... these boilers have a strange quirk that can cause the pcb to revert back to its 'european market' settings and cause the boiler NOT to give more that 41 degrees to the DHW - its the european anti scald feature.... if the display will NOT go above 41 degrees irrespective of the temp when you turn it off, then its a possibility, especially given the age of your boiler as it was the older ones most susceptible to this...

 

[DP]

Boiler has two thermistor. Might be an idea to measure the resistance. Failing that, replace both.

I suspect the primary thermistor to be the culprit

 

[3continentsplumber]

I had a similar problem with a Britony boiler. Again replacing the thermistor did not help.
If there is gunge in the central heating circuit, some of it can find its way into the secondary heat exchanger that heats the hot water. The small water passages become blocked, obstructing the flow and causing it to overheat. The hot water then becomes hotter and hotter until the thermistor does its job and shuts the boiler down to prevent further damage.
What you need to do is to either flush out the secondary heat exchanger or to replace it and before you put the boiler back into operation, flush out the central heating system. This probably means a power flush and maybe fit a magnaclean filter to prevent reoccurrence. Sorry buts its not going to be a cheap solution.

 

[DP]

3continentsplumber, read the replies.

It has already been established the primary water does NOT overheat, therefore, boiler is not shutting down due to high primary temperature (60 degrees C is normal. I would expect 70 degrees when boiler set correctly; overheat is 95)

Dave and a few others have suggested primary thermister be changed. Try that. Also, has anyone 'worked' on the boiler recently in the PCB area? If yes, is that when the HW problems started?

 

[PUTWADE]

DP; thanks for the reply. Just to recap on my boiler:

1 Over a few months my Linea 36HE has started running hot then cold with DHW demand.
2 Saturday; Engineer replaced secondary thermistor - fault returned.
3 Monday; Different engineer (same firm) cleaned muck from condensate trap - fault returned.
4 I tested temperature difference at 40C DHW by turning off tap and noted the resultant primary temperature displayed at 60C.
5 Tuesday; Different engineer (same firm) phoned to say the problem was definately the PCB. I queried if it could be the primary thermistor or HE and he said no chance. I haven't asked him to come out yet.
6 Tuesday night, I drained down the system and flushed some clean water through it before re-pressurising....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 before display fault code 10 (no flame detected) and requests a reset. This just cycles. I assume I've got some air in the pump which is causing it to fail, (I'll try to clear this later).

You mentioned PCB in your last post but no, there has not been any work on this item, only what's listed above.....shall I replace primary ntc sensor in the meantime unless you think otherwise?
GW

 

[DP]

PUTWADE, start a new thread. You boiler is not the same as the Linea 28. Information, while some will be similar, a lot of components are different. For instance, your boiler has two thermistors on the primary circuits at the main HE while Linea 28 only one.