Hi all,

Can't get hot water from out 820/20T unless the CH is on too. When set
to DHW only, main burner doesn't ignite.

The fault-finding flowchart in the manual says:

Are microswitches on shunt valve being operated mechanically?

If NO, check/replace 3-way microswitch.
If NO, is flow rate 3l/min?

If NO, check filter flow.
If YES, replace 3-way valve.


Firstly, are the "shunt valve" and the "3-way valve" the same thing?

Secondly, one of those first two NO's should be a YES. Should that be
the second one (ie. If YES, is flow rate 3l/min?) ?

Thirdly, how do you check whether the switch is being operated
mechanically? It's on the back of the 3-way valve which is at the back
of the boiler behind a rat's nest of pipes and wires. What should I
expect it to do and is it possible to check without removing the whole
valve first? And if I remove the valve first, will it still do what
it's supposed to do with no through-flow?

Fourthly, I got the last 3-way valve from Travis Perkins a few years ago
as I had an account at the time, but any recommended alternative
suppliers?

Thanks for any help,

Mike