I have had my back boiler and storage tank replaced with an Ideal Isar
35combi-boiler. Previously I had a pressure pump serving my bath and
shower via a thermostatic mixer unit. My installer told me that the
Isar would not cope with the flow rate of the pump and removed it.
The bath water now delivers about a litre of hot water, with the valve
selected to fully hot then runs very cool for half of the bath full. It
then runs hot but to get the bath water hot I have now to drain off the
cold water in the bath and start all over. Even then I cannot
guarantee that the hot flow will continue. I now run the bath until the
water gets cold then I run the hot tap in the wash basin until the
water gets hot, then continue running the bath. Sometimes I have to
repeat this procedure several times. The installer says that this is
normal for these boilers, so I called in the Ideal Heating engineer.
He confirmed that I have sufficient flow and pressure and that I have a
problem. His solution is to remove the thermostatic mixer and fit
conventional taps. Is it possible that I can get a back flow from the
cold supply at the mixer back to the boiler, which now supplies this
cool water back to the bath. The wash basin is fed by the same system
that runs the bath and generally has slightly higher temperature than
the bath when this is running cool.
I am reluctant to replace the mixer (which I like) and fit a separate
shower circuit, unless I can be assured with a logical explanation,
that this will definitely cure the problem. Has any one else had this
problem and have solved it. The central heating system is OK.