hot water problems

[ackers52]

This concerns central heating with 2 settings:
1) water only 2) water and radiators
When water only is set, water heats satisfactorily.
When water and rads are set, rads heat but water is tepid only. It seems 90% of heat goes into radiators.
System has worked for over 15 yrs with hot water and rads on setting 2. This problem only recently arisen.
There appears to be no air in system as hot water arises on water only
setting and rads heat well on water and rad setting.
Anyone know cause of this problem and/or how it can be solved.
Thanks

 

[Softus]

Rad valves open too wide? Faulty motorised valve? Faulty programmer? Combi boiler with faulty diverter valve?

 

[ackers52]

Thanks for suggestions,
Have tried half closing rad valves, don't have motorised valves, and not a combi boiler. Maybe the programmer? - any way of checking this?