I hope someone can help me I have recently installed C/H in my bungalow I installed everything myself but not the boiler but when the boiler calls for hot water there is one bang it seems to come from the diverter valve but if I get the wife to switch hot water on with programmer no bang also when calling for hot water and heating more than one bang it bangs once every 4-5 minutes. The system is sealed with hot water tank mid position valve and the boiler is A grant vortex external oil boiler 6 reds 5 with TRVs