Central Heating

[Reg-plumb]

I have a Vaillant 240 VCW XH Combination Boiler and it is 12 years old.
I have replaced the Main CH Heat Exchanger and the Diaphram including the Diverter.

The problem is when the CH is on and DHW is drawn at the same time.
Once DHW Tap is closed then the boiler shuts down including the pilot light. The pilot light is then re-lite and CH fires up as normal.

Can anyone please advise me. (Kev-plumb where are you, Sir).

Thank you very much for replying. If there is a problem with scaling where would it be in the boiler?, as I have cleaned/flushed out the Main Heat Exchanger, Diverter and DHW exchanger.

Can anyone please advise me

 

[B.O.B DOLE]

I have a Vaillant 240 VCW XH Combination Boiler and it is 12 years old.
I have replaced the Main CH Heat Exchanger and the Diaphram including the Diverter.

The problem is when the CH is on and DHW is drawn at the same time.
Once DHW Tap is closed then the boiler shuts down including the pilot light. The pilot light is the re-lite and CH fires up as normal.

Can anyone please advise me. (Kev-plumb where are you, Sir).

had simiar prob on a brittony it turned out to be the ch flow switch

 

[chrishutt]

had simiar prob on a brittony it turned out to be the ch flow switch

Britony doesn't have pilot light, Vaillant doesn't have flow switch. So much for "similar".

The problem is that the heat exchanger is overheating and the overheat stat then cuts the continuity of the thermocouple circuit. Overheating possibly due to slow response to end of DHW demand?

 

[Agile]

Overheating AFTER hot water usage is usually either due to scaling up or the failure of pump over run when its provided.

Tony

 

[Reg-plumb]

Thank you for your replys.

Where would I locate the build up of Scale?. I have Cleaned and Flushed out the Main Heat Exchanger, DHW Heat Exchanger, Diverter Assembly, Water section diaphram linked to the servo control and control/connection lines to the Diverter. The Flow rate is ok.

All replys would be very appreciated.