I just turned my heating on (have combi boiler, not sure of make think Triton, less than 5 years old). Now, when I have a shower the water runs very hot, then cold, on and off. The temp gauge on the boiler seems to shoot up, then the gas cuts off. Heating works ok, but if I've had the hot water and heating setting on all day, it registers the temp of the radiators as high, even when they are cold and won't heat them up, unitl I turn setting back to just radiators and then it fires up.
I called a plumber and he said it might actually be the shower mixer tap that has a problem with it, not the boiler. Bit confused. Any ideas what I could do to decide if I need a mixer tap fixer or a boiler fixer....