No Hot Water

[Windinherhair]

Hello folks,
I have a Potterton Suprima boiler feeding an open, garvity fed heating system. The heating is fine, hot radiators ground floor and first floor. When running on hot water only I get "kettling" sound at the boiler and then banging pipes. The hot feed from the boiler to the hot water tank is hot but the return is stone cold. If I then switch to heating and hot water I hear a swooshing noise in the pipes and the banging noises disappear. I have replaced the auto air vent which is off the hot tank to boiler return. I have replaced a leaking central heating drain valve and I have drained the system a few times. I have gone round tapping the pipes around the hot tank while the system is on to try and dislodge any air-lock. I also tried attaching a hose to the drain point and applying mains pressure to try and force air through the system. Last weekend I drained the system again and added sludge remover to try and clear the system a bit. I have had this issue in the past and managed to get it going by combinations of the above but this time it is being really stubborn. I think the next step may envolve a sledgehammer........
Cheers, Iain (Mr Windinherhair)

 

[frhp]

hi mate,

the system you have, i believe has 28 mm gravity fed hot water pipes to the cylinder. the reason you can hear the kettling noise from pipes, seems, the pipes coming back to the boiler from cylinder (28mm) are badly blocked.

a very strong flush (ideally a power flush) can possibly solve the problem. otherwise.... u might need a new system....

it is mainly the blockage causing bad flow. coz it has no force behind the flow.. hence...

 

[spraggo]

Check that the small header tank in the attic is at least one third full of water and that the float valve is not stuck.

 

[simond]

Have you tried shutting the AAV? If it is in the wrong place it will draw air into the system each time it starts, creating an airlock.

You can still open it when the pump isn't running to purge any trapped air.

 

[Windinherhair]

Hello again.

Thanks to everyone who replied.
I tried the power flush at two different points in the system to try and make sure it was effective. This made a slight difference, now having tepid hot water. Removed connections to flush hot water tank feed and return alone when I stuck a pencil in the pipe and found a dirty great blockage, two inches from where I had first connected the power flush unit ! The block was at a T junction so the water must have been bypassing the blocked pipe and taking the path of least resistance. Wonderful - heating and hot water but the next night the pump packed in - had to dismantle kitchen cabinets and pull up part of a tiled floor to replace it. Anyway, now going fine.
Cheers, Iain (Mr Windinherhair)