Blending water for a shower on a low temperature HW combi

[Ltnman]

My new combi boiler is set for a hot water flow rate of 42C to avoid paying for HW only to add cold. 42C is a good compromise.

For years now I have suffered from a variable shower temperature with the HW set at 60C so I have decided to bite the bullet and change the shower mixer bar.

Looking at one set of instuctions it states:

"The hot supply temperature MUST remain a minimum of 10°C hotter than the required blend temperature for optimum performance"

Is this standard on all mixers? What happens if I don't? Do you guys have any problems?

 

[jeff the gasman]

“Must” sums it up.
It means it has to!

 

[Johntheo5]

My new combi boiler is set for a hot water flow rate of 42C to avoid paying for HW only to add cold. 42C is a good compromise.

For years now I have suffered from a variable shower temperature with the HW set at 60C so I have decided to bite the bullet and change the shower mixer bar.

Looking at one set of instuctions it states:

"The hot supply temperature MUST remain a minimum of 10°C hotter than the required blend temperature for optimum performance"

Is this standard on all mixers? What happens if I don't? Do you guys have any problems?

You won't pay any more for heating the water to 60c and adding cold water than just heating it to the required showering temperature.

The shower probably will work OK even if you run the combi at the required showering temperature and don't add cold water, the main reason for the dT difference of 10C is to ensure tight shut off of the hot in the event of cold water failure/shut off. The Mira Excel EV says,

"The wax capsule sensor effects a shut down to seepage in approximately 2 seconds if the cold supply fails. Shut down to seepage is only achieved if the hot supply is 12°C above the blend temperature"