vaillant combi boiler, hot water tepid in shower and bath

[sd37]

Hi, the problem....

Vaillant combi max turbo boiler, the heating is fine. The hot water was fine until a few weeks ago. First the shower started to run tepid unless the flow turned low, then the bath tap did the same, now the basin tap is going the same way. Hot water to the kitchen is still piping hot.
We have called out 2 plumbers, first replaced the diverter valve which did nothing to improve the situation. The second suggests the problem may be with the thermostatic valve on the shower, but how does that explain the bath and basin water supply

Any ideas or explanations??

[tonyg]

Hi
We have a similar broblem on our combi (not the same manufacturer)
We find every winter when the outside temperature drops so does the domestic hot water temperature,we just run the water more slowly which make the temperature more acceptable and live with it. It's OK in the warmer months(if we get any!)
We've been told to fit a bigger boiler when we come to replace it
Sorry I can't help

[sd37]

hello, thanks for your reply. One of the plumbers did mention that as a possible cause, but I wasuprised as I had never heard of this before, and it hasnt really been that cold yet this year, what happens when ithe weather gets really cold!!! Not sure I can afford a new boiler.....
Is there anyway of restricting the cold flow to the bath mixer tap perhaps to allow more hot through? Another suggestion was to fit non return valves to the hot and cold pipes, this meant nothing to me, can anyone explain how that might (or might not work?).