ketteling boiler, but only when HW on and CH off?

[Hazelb]

My system is a tank fed system, with 2 heating zones and a HW loop, each isolated by a 2 port valve.

When just HW required a lot of protests form the boiler! ....thumping, banging and won't fire up. Will be fine with CH running.

I can also hear a lot of cavitaion (?) in the pump when that starts up.

I think I've got air in the system and I suspect that the auto air vent only works eficiently on the CH circuit.

How can I bleed air from HW side ot system? There is one rad( towel rail) on the circuit and the HW tank, that is all.

Do I need to bleed the pump? (how?)

Should I be able to find a bleed point in the boiler? ( Baxi solo about 15 yrs old)

Should I fit an auto air vent to the towel rail?


Let me know if I'm talking tripe!

 

[seco services]

the pump won't need bleeding if ok on heating is the pump running on hw only.

is the return from the cylinder hot or cold ?

 

[Hazelb]

the pump runs ok on hw and the return pipe is hot.

The rad on the HW cirut is hot (not coldat the top)

When the system is cold and HW comes on first, rather than CH........... thump bang wollop!

2 port valve and pump seem to act correctly for HW, ie pump running, valve open.

Its almost like air collects in the boiler, with just HW running?

if I run CH first for a bit then HW no problem!


Could the boiler setting/control nob be set too high? What should it be on?

 

[75pete]

On your hot water tank do you have an isolation valve on the heating circuit. If so it could be only part open giving you your problem. Also you should have a bleed point for air.