Highflow 400 not heating when CH running

[masaccio]

Our Highflow 400, which has had a series of problems now has a problem that Worcester Bosch have tried to fix but not succeeded. They plan to have another go, but I wondered whether anyone had some theories here.

When the central heating is not running, the boiler can deliver hot water to the taps. But with the tap still running, you can flip on the CH and the water runs cold. Turn the CH off and the tap gets its hot water back.

The heat exchanger at the back of the boiler was switched out on the last visit, but that hasn't solved the problem. It was powder flushed a couple of months back and had inhibitor added.

Thoughts anyone?

Jon

 

[reg091]

I too am having problems with a WB Highflow 400 and having downloaded the installation and commissioning instructions have an idea of how it should work. The relevant info for you may be this:

"The appliance will supply heat to the central heating system as
required. A demand for hot water at a tap or shower will override the
central heating function for the period of the domestic hot water
demand."

Suggests to me that this is not happening with yours. So whatever controls the diverting of the hot water from CH to HW may be the culprit. Sorry that is a bit vague but hope it helps.