Central heating pressure is going too high? seems to go above the pressure relief valve setting and the overflow is constantly leaking..
Is this the diverter valve passing into the central heating system? and if so can it be repaired?
The other thing that seems to be happening is that the hot water seems to run hot for 30 to 60 seconds then go cold for 10-20 seconds and this repeats continually when it is running? the selector is set to prioritise the hot water flow.

Any help!