Gulfstream Class A

My Gulfstream will always turn on the central heating at the same time as heating tap water.
There is switch to select HW or HW+CH.
I have it set to HW only.

I have a timer set to heat water and flat twice a day, In the winter I select HW and CH, but now as its warming up I've selected HW only. However, now the CH is still coming on.

This has only started happening recently, and I can't get hot water without the CH being engaged.

Any tips?

I have been having a similar problem with my A Class and I think I have narrowed it down to the 3-way diverter valve sticking. This would normally divert the flow of heated water to either the heating system or the hot water system. Mine appears to be sticking somewhere between the two settings and thus not fully isolating the radiators when just hot water is required.

I have managed to carry out a temporary repair by removing the actuator head and using a pair of grips to work the spring-loaded valve assembly in and out to free it off. This seems to have solved the problem but I think a replacement part will be requied for a permanent cure.

I believe a replacement cardridge is available for the diverter valve which means that you will not have to replace the whole valve assembly.