Halstead finest gold

[AideyJ]

Was called to one of these last week that had no heating or hot water, discovered a problem with diverter valve so changed diaphragm and put in a new inner service kit. Hey presto problem solved or so I thought.
This week called back again to no heating/HW. Went round again and found that the boiler worked when the external timer was set on constant for both heating and HW but when you put it on timed neither worked! All the pins were moving across as they should but boiler wouldn't fire up but put it on constant and everything was hunky dory again.

Any ideas?

 

[lame plumber]

check timer output are correct!

 

[aggis]

Is it wired up correctly, it needs a permanent live, as well as switched for heating, check you've got 240v all the way to the circuit board, then to the dhw micro switch