boiler has no hot water

[bluesky]

been called by a friend, he has a vaillant turbomax 242e, he said the boiler only works 5 seconds and then have a rest of about 5 seconds, so there is no hot water, i got there and checked:
1. air switch is fine,
2. rectification lead is ok,
3. pump is running
4, i noticed that when the boiler runs for 5 second the water temp goes to 90 degree very quickly and then the flame is gone,
5, thecked the secondary heat exchanger, it is very cold, looks no hot water goes through,


i am thinking the divert valve is wrong, shall i change it?

cheers in advance

 

[Blake]

If it's the boiler i'm thinking of, unscrew the head on the Div valve to remove the motor and see if the plunger is moving or not. The motor could be knackered or the valve full of crud.

Failing that, ring there tech line, you don't wanna go changing parts without knowing what the problem is first otherwise it could get expensive.

 

[Billy Bob Bob]

if its racing up to 90 degrees plate heat exchanger blocked or diverter valve faulty if its the boiler i think it is refurb kits available for the dv,but my first thoughts would be the plate heat

 

[diamondgas]

I'd be thinking along the lines of plate htex too. Does the appliance work okay in C/H mode? If not then its pump or serious blockage within the boiler circuit/heatex Id think!

 

[stevetheplumber]

pound to a penny its the heat exchanger assuming its working in heating mode if not then pump or blocked main heat exchanger

 

[Kengasman]

As above, sounds like plate h/e, often cheaper to replace it than flush it out

 

[merv]

I had a simular problem recently on a VCW 242 E and it was the NTC flow sensor.

 

[bluesky]

i tried the heating mode, the radiators were hot, but the boilers worked the same way: 5 seconds lit, 10 seconds off, then on again, the temperature rushed to 90 degree and dropped bit, then rushed to 90 again....

 

[diamondgas]

WOW!!!!
Forget plate htex!
Rushing to 90deg indicates that the heat is not being removed from the appliance (pump/blockage) what's the temp difference between f&R pipes? best checked cold! You'd prefer a gradual rise in temp on the flow rather than rapid, that'll indicate decent flow of water through the boiler! Incidentally, pumps can spin merely but their impeller can become dislodged! It's not always simple alas!! lol

 

[bluesky]

hi diamondgas, i think the pump works fine because the radiators were quite hot...