Vokera linea 24

[RossMac]

I have a vokera linea 24, the central heating is working fine, however the DHW has started to play up. (ie) turn on a hot tap boiler fires up runs for 30 secs to 60 secs then the burner cuts out the temperature drops on the display and the burner will cut back in. if in the shower water will be hot then cold etc.
I have changed the hot water thermister part number 8484, this made no difference.

the thing that confuses me is that just before the burner cuts out the needle on the pressure gauge for the central heating starts to bounce a bit. and when the burner cuts out it steadies again.
(don't know if this has any relevance or not but it dosen't happen any other time)

can anyone help ??

 

[gas4you]

Plate heat exchanger will be blocked on the system side

 

[RossMac]

how do i prove / repair this .
is it a big job ?

 

[gas4you]

When the boiler cuts out, quickly turn off the hot tap. If display is reading 90 + then it sounds like my previous answer.

 

[RossMac]

yse dave , i did this and as you say the temp was i think about 88.
so assuming this is the problem , what do i need to do to repair.
Thanks
Ross

 

[RossMac]

Dave carried out this check again just to be sure, and when i turn the tap off a couple of secs after the burner cuts out, the temp was 88 on the display, i then turned on the heating the flow pipe went instantly hot for a couple of secs then the temp display dropped. is this normal?

Ross

 

[gas4you]

Replace the DHW plate heat exchanger, or at least remove and try to clean out.

trouble is though that the system will probably be dirty as well, so unless you flush out system new plate he will block pretty quickly as well.

Simple job on these, only 2 screws to remove plate he.

Follow your MI's.

 

[RossMac]

thanks very much for your help dave, will let you know how i get on,

Ross

ps, the system shouldn't be to dirty i think, as all rads and pipework were new 4 years ago and i flush it out every year and fill with fresh inhibitor.
the problem probably lies in the fact that the boiler was existing so could be 8 or 10years old, and the system was probably never drained until i bought the house.

 

[gas4you]

What you are describing is normal.

The problem you are getting is caused because the plate he is blocked on the system side so therefore the water in the main hE is being heated at full tilt but the blockage is preventing the heat being transfered to the domestic side of the plate he fast enough, hence the overheating.

 

[bengasman]

Replacing the h/e or cleaning it will usually only help for a while. Flush or powerflush is what you need. What you do every year is not a flush but a rinse, pointless exercise

 

[RossMac]

removed hot water heat exchanger, and blasted the garden hose through it, (8.5 bar mains pressure) and got some black debris out, re-fitted and all seems to be ok for now.

if it becomes a problem again, i will get the system power flushed and fit a new heat exchanger.

Thanks for all your help

Ross

ps just incase you are thinking 8.5 bar is to high, i have a PRV on the cold water inlet to the bolier to reduce the inlet pressure to 3bar.

 

[bengasman]

if it becomes a problem again, i will get the system power flushed and fit a new heat exchanger.

if you get a proper powerflush, the heatexchanger will be clean too