Vaillant VUW GB 242E - No CH but HW fine.

[RichardGC]

Hello forum

I have a Vaillant Turbomax VUW GB 242E (black panel with green knobs) which has been extremely reliable but has recently thrown up a problem.

Hot water side of things works perfectly, but when demand for central heating is made the boiler does nothing at all….it just plays dead.

Having researched as much as i can I have tested the external controls and eliminated them (putting a jumper across two terminals as described in manual). I have also followed troubleshooting and replaced the main board but no joy.

The diverter valve was replaced a year ago and appears to be working perfectly and in addition the flow switch and connecting pipe is clear and appears to operate as it should? Pressure is at 1.4 bar.

If i set the heating to demand and manually hold the diverter valve switch down then it fires up fine and and circulates the water around the rads fine, which must eliminate the fan and pump?

One further point…. When i turn the boiler on something make a ‘clonk’ and simultaneously the flame light (not the red lockout) briefly illuminates. This may be normal but i rarely switch the boiler on (usually always on) so cannot remember if it should do this?

Im puzzled by this one as a lot of components seem to be working fine for hot water.

Any thoughts much appreciated.
Thank you in advance

Richard

 

[Stuckinarut]

So if you're pressing the microswitch down and the boiler fires, then that tells me it's the microswitch not being made, possibly pin not fully extending?

 

[RichardGC]

So if you're pressing the microswitch down and the boiler fires, then that tells me it's the microswitch not being made, possibly pin not fully extending?

The hot water works fine and the pin extends and everything fires up as expected. Its when central heating is demanded nothing happens, unless i manually trigger the microswitch.

 

[Stuckinarut]

unless i manually trigger the microswitch.

So if you're pressing the microswitch down and the boiler fires, then that tells me it's the microswitch not being made, possibly pin not fully extending?

Answered your own question there but then telling me it's fine? Are you pressing the pressure differential switch?

 

[RichardGC]

Ah…sorry, i thought you were referring to the Diverter Valve one. Thats the one im pressing which makes central heating fire up.
When i press the diverter valve switch the boiler fires up and the pin in the pressure switch lifts up quickly and returns following the pump over-run on switch off, so that would indicate its ok?
Thank you for your responses