hi have just had a call from my sister in laws and she has a problem with her boiler.All i know it is a glow worm combi about 5 years old she has hot water but no heating.Would i be right in thinking it would be the diverter valve at fault and if so can you get service kits for them. what would be the best way to test dv valve ? thanks for any advice.Iam just aplumber not heat eng so please be gentle with me thanks peter