ecoTEC838 Vaillant boiler temperature spike shutoffs

[Joost Dantuma]

Hi,

We have an intermittent but common fault on our 7 year old ecoTEC838 Vaillant boiler.

When running hot water, the water temperature will suddenly spike to an auto-safety shutoff point (over 80 degrees). We get "overrun" errors "water Deficiency" errors. (Specific errors: F20 "Temp Limiter", F24 "Temp rises too quickly").
Sometimes when the heater shuts down, there is a large thud. There is also sometime light metallic tinkling sounds as the water runs through the system.
We were advised this was because we're missing a magnetic filter and that rust is blocking the boiler.
I believe this but We're being quoted £900 to powerflush the system and add a filter.
Is this reasonable? Is there a simpler (cheaper) explanation/fix?

Thanks in advance!

 

[Dan Robinson]

The cause is likely sludge.

If it's then it'll need dealing with, although if it's got into the main HEX then chances are that'll be goosed and powerflushing won't help.

As to the cost. We don't know. This isn't moneysupermarket.com, we haven't seen the house and you haven't given us much information.

 

[Joost Dantuma]

Thanks Dan.
Don't know what info you need: 3 floor London terraced house. 14 radiators (from memory) (Including bathroom & shower room towel racks).
Sounds like it is needing a purge then ("sludge"), and that £900 is not crazy.

 

[AGAS]

Might want to change the pump