Worcester 42cdi Hot water problem

Hello,
I have a problem with my Worcester Greenstar 42cdi. It was working fine until yesterday. when I noticed that the hot water would not get hot. upon further investigation, I am even more baffled.
The boiler is in the upstairs bathroom.
1. Bathroom sink, (closest to boiler) gives warm water.
2. Bath, warm water.

If I run both taps at the same time, the bath tap goes cold, but the sink tap gets hot. I cannot get the bath tap to give out hot water. Also no hot water from the kitchen sink.

Any help greatly appreciated as wife is frustrated!

 

Got any mixer taps?
Try isolating the cold inlet to the boiler and see if you still get water out of any hot taps.

 

Ive found the problem!...
the garden hosepipe is linked to the hot water system, It was fitted a few years ago but never been used. It is connected under the kitchen sink, (hot and cold merge into the one pipe which goes outside to the hosepipe).

I switched the hot on to fill the swimming pool for the grand daughter and forgot to switch it off afterwards. Obviously, it is not a one way valve as when this valve is open, the cold water is running into the hot water pipe.
What type of valve should this be?

Thanks for your help

 

Deleted.

 

You need double check valves on the hot and cold feeds...

 

You need a pressure equalising valve or a blending valve

 

oh bless him

 

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