My Vaillant Turbomax Plus boiler is having problems supplying hot water.
The central heating is fine but the hot water,though it
works,intermittently goes cold. I first noticed it when using the
shower, I thought at first that the shower was at fault, however on
checking it also happens when running the hot taps. I have checked that
no one else is calling for hot water at the same time and have tried
adjusting the water temperature to no avail. At a guess it runs hot ok
for about 20 seconds then goes cold for 10 seconds. Any ideas please?