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Baxi backboiler / radiator questions

Postby mantamark » Tue Jan 11, 2011 8:02 am

Hi all,

We have recently moved house, went from a flat to a semi, flat had a combi boiler, house has an older back boiler system.

It was fitted in 1998 and is a baxi system with tank in loft, cylinder in bedroom, boiler behind fire.

I have drained the system, used sludge remover, left for a week, drained & filled with a inhibitor, read how to do it on the net, fairly confident with diy stuff or i would ask a pro.

Few questions...

1) This was happening before the clean, but seems to be worse now, can hear air rushing through certain (not all) rads every now & then, why would this be?

2) When the hot water is on, the rad in bathroom & bedroom that has cylinder in heat up, why is this? Is this normal?

3) The same two rads constantly need bleeding every few days, i do this when the system is cold, but its very annoying to have to keep bleeding, i'm assuming air is getting into the system, but a) why only these two, and b) how do i diagnose?

Thanks, any additional info needed, please ask.

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Simply Build It

Postby htg engineer » Tue Jan 11, 2011 7:09 pm

It is common for upstairs radiators to get warm when heating is on - with gravity systems. You can form a trap (U) shape in the heating flow where it comes off the boiler to prevent this.

Air being drawn into system - could be, check pump speed and check valves are not leaking, if pump on III try II.

The radiators could just need bleeding because the system has been drained recently - there could still be air in the system after re-filling - this could also be the cause of the sound of air in radiators, leave a for a few weeks - bleeding radiators as necessary see if it improves.l

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Postby mantamark » Sat Jan 15, 2011 6:34 pm

Thanks for that, had a look at the pump & i cant see anywhere to adjust it? its behind a few pipes accessed via a hatch in the chimney breast? just looks like an inline pump on one of the pipes.

New problem now though, replaced the thermostat, same make, just newer & now digital, set up as per intructions & wired in correctly. (used same two wire setup as old stat)

Now when the water / heating comes on(old system so have to have water on for heating to work), there are loud bangs & the sound of bubbling water coming from behind the fire & in the airing cupboard, this never happened before, so we are wondering how just changing the stat can do this?

Thanks for any help.

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