boiler keeps getting air locks, why?

[dave144]

I've just moved into a house with a Baxi Boston floor standing open flue boiler. Ive only been in the house a month and have lost all hot water twice due to air locks in the cylinder. Any advice as to how and why this keeps happening? A family relative who is a plumber has suggested pressurising the cylinder to do away with the cold water feed tank.

I've always had combi's so this thing is alien to me. Maybe time to invest in a combi system?

[dave144]

The water gets cooler each time it is demanded not always from running baths. The central heating gets red hot even though there is no hot water We get by with as we have an electric shower but is still less than ideal.

I have tried everything and I mean everything!!! Bled all the rads with the system shut down starting from bottom to top. Then putting the cold water feed from the washing machine onto the hot to push the air out..still nothing. Have tried twice to crack each union around the cylinder resulting in me getting soaked each time. I will try to get a few pics of the shoddy home built system tomorrow.

About mid way up the cylinder is the overflow with a bleed point, tried that too but yep you guessed it still nothing.
As an Engineer it pains me not to know how to fix something so simple. Got the wife's uncle whos a plumber coming round, so fingers crossed. Do you think pressurising the cylinder is a good idea?

[dave144]

It's a gravity fed hot water system. The hot water outlets pipes from the boiler get scalding hot but the airlock is causing the stat to trip out I think? Either way the hot water never reaches the tank.

[dave144]

How the dickens do you remove the sludge? Thanks for the diagram. Sounds like when I was robbed by the last plumber all he did was get the sludge moving and now its settled again.

[dave144]

I still get cold water from the hot tap when the darn thing plays up.

The idea of the hot and cold washing machine feeds is that the cold water is a higher pressure than the hot and "should" push the air lock up and out into the cylinder cold water tank. Lots of people swear it works, not convinced myself.

[dave144]

Well had the plumber out who's the wifes uncle and he put it down to a number of factors.
First was the fact that the cold water feed to the tank was not high enough above the cylinder. Second was the shocking DIY installation by who ever fitted the system way back, with some of the pipe fittings only hand tight. The pipes feeding the coil in the cylinder had limsescale deposits at the joint with the cylinder indicating a leak at some point.

He got us up and running again by "boiling off" the cylinder? didn't ask too many questions as I'm going to replace it with a combi now. The cost to pressurise and replace the cylinder isn't far off what the cost of a new boiler will cost, bearing in mind we'll get it at a "family price"

[dave144]

How do you short the stat? I wasn't around when he sorted it.

As you say I don't think there was any sludge in the system but because the cold water tank isn't high enough above the cylinder it will keep drawing in air. The tank is as high you can go, so where to got from here??

[dave144]

The cold water tank.



Doesn't look pretty does it?


Not a simple fix

Still waiting on the wife's uncle to get us a quote...family for you

[dave144]

Quick update. Another week another air lock and no hot water. Sorted it myself today by turning off the CH and switching on the hot water pump without the thermocouple fitted for about 20 mins . Not the best solution but it sure as hell worked.