No hot water but the heater works

[Mark Tayler]

Hi all, I am having an issue with my hot water system.
the heating seems to work ok, just the hot water to taps stopped(getting hot) suddenly.
The system is a Vaillant gas boiler with an electric heated immersion tank, Thermostat is a PTT2, which no longer available to buy and no know replacement. The system has two motorised flow vales, I believe they work, but I mechanically opened them anyway, so not the issue.
after fiddling i have got the the thing to warm up to 40c a few times, then it just reverts to about 30c as seen on the boiler gauge.

PS the Vaillant guys say the boiler is ok but is not getting the signal to fire up…
help
cheers Mark

 

[ianmcd]

Manually opening the zone valves will not send a signal to the boiler to come on, manually open the HW zone valve and latch it open then switch the CH on and turn up the thermostat, once the boiler comes on feel the outlet of the HW Zone valve and if it is now getting hot then you need to change the actuator or valve depending on what you have