heatline vizo boiler no dhw

[keyringken]

hi, we have just moved into a house with a heatline vizo combi boiler.
the centeral heating is fine. but the hot water has a mind of its own, some times it does and somes it don't ignite. when it does you have to turn the water down to get it hot then its a fine line between to far it cuts out to high and its cold. any ideas why its so semperamental on igniting??

 

[Llan1observer]

depends how old system is,
but could be pump, diverter valve or plate heat exchanger are full of sludge causing it not to work

 

[Agile]

I think the DHW flow switch may be failing to respond as well as a rather blocked plate HE.

But it could be several other causes. Without seeing it I cannot be more definitive.

Tony