[SV650rules]

Combi boiler pretty much twice as complicated as a normal boiler. Has separate heat exchangers for CH and HW with the added problem of the pressure switch that is supposed to sense when a tap or shower is turned on and fire up the burner, but can be very temperamental. Combi also only good with smaller properties with only a few possible hot water outlets. I replaced our 20 year old pressurised Vaillant mild steel glass lined hot water tank last year with a Sadia- Heatrae stainless tank. Got fed up of replacing the sacrificial anode at £50 a pop, and worrying when tank was going to corrode and flood the house. Had a glass lined mild steel tank fail in one house and it made an awful mess, never trusted them since. Mind you the tank failed in a soft water ( acidic) area, hard water is much less corrosive, even copper pipes do not survive as long as they should in soft water and develop pin-holes - not good news. Good news is that we now live in hard water area.