no hot water,boiler wont stay on

[clumsy1]

Hi my partner changed the bathroom radiator yesterday, draining the system first. However, once he had finished and we turned everything back on we discovered we had no heating or hot water. we have a potterton nettaheat boiler which comes on for maybe 5 mins then clicks off. We kept bleeding the radiators and managed to get the heating to work but we still have no hot water. I have checked the hot water tank in the attic which is full but the smaller tank inside it has a small amount of water in the bottom, I have looked for a ball valve on it but cannot see one...there is just a cone which does not move on the bottom of the tank. Am really baffled....all was working fine before we changed the rad so am assuming it is something we have done. I know that the rads were not drained in any specific order does this matter? Have bled them all again and they seem fine. have we missed something somewhere???

[toscal]

It could be some debris has got stuck in the 3 way valve so that its sticking in the heating only position. If its a combi boiler then this valve is somewhere in the boiler. On my combi its actually a diaphragm type valve and it got stuck in the hot water only position once. Had to call the service guy out. But it wasn't that expensive, but it was also quite a while ago now.

[clumsy1]

its not a combi boiler so where would the valve be?? There is a pump in the airing cupboard.

[JimNoble]

Hi my partner changed the bathroom radiator yesterday, draining the system first. However, once he had finished and we turned everything back on we discovered we had no heating or hot water. we have a potterton nettaheat boiler which comes on for maybe 5 mins then clicks off. We kept bleeding the radiators and managed to get the heating to work but we still have no hot water. I have checked the hot water tank in the attic which is full but the smaller tank inside it has a small amount of water in the bottom, I have looked for a ball valve on it but cannot see one...there is just a cone which does not move on the bottom of the tank. Am really baffled....all was working fine before we changed the rad so am assuming it is something we have done. I know that the rads were not drained in any specific order does this matter? Have bled them all again and they seem fine. have we missed something somewhere???

It sounds like you could have an unvented cylinder there. In which case the small tank on top is actually an expansion vessel, and the "cone" is a tundish.

Unvented cylinders require either a pressure vessel or air gap at the top to accommodate expansion of hot water. If either the pressure vessel fails (or isn't pressurised correctly) or the air gap is lost, I believe it can result in no hot water flowing.

If that's what you have, I would advise getting it looked at/serviced (the manufacturers generally suggest getting it done annually). Unvented cylinders have some quite nasty failure modes if not properly maintained (if all the safety mechanisms fail, they can go bang quite spectacularly)...

Jim