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Radiator fills up with air when hot water comes on!

Postby techysci » Fri Oct 17, 2008 6:21 pm

Does anyone have any suggestions as to why the radiator on my landing sounds like it is emptying its water every time I turn on the hot water. It is the first radiator connected to the boiler. It does not just sound like it is emptying when I bleed it, it is usually practically empty of water. There are two other radiators upstairs that need regular bleeding too although not as badly. No problems with the others. It is not a sealed system.
Thanks in hope.
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Postby plumbbob » Fri Oct 17, 2008 11:03 pm

You haven't said what type of central heating system you have so any reply is going to be guesswork, but the most likely cause is the you have the common problem of a poorly designed system where air is drawn down the expansion pipe and into the first radiator. Although this may cause other problems, try turning the pump speed down (If you can). If this stops the air being drawn in, consider having the plumbing altered.
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Postby Steve the gas » Sat Oct 18, 2008 4:37 am


Check your small tank in the loft - to make sure there is water in it and the ball valve is working correctly.

Steve the gas
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Postby techysci » Sat Oct 18, 2008 6:15 pm

Thanks for the posts. I've checked both the feed and expansion tank and the cold water tank levels and they are fine so next I'll try the pump speed which has three speeds (currently on no.3). It is a gravity fed, pumped system using a floor standing Mexico boiler.
The whole system seems to have to decided to go on the blink this autumn.
The thermostat on the HWC doesn't seem to be working so the hot water is coming out at blistering temperature.
The overflow pipe from the feed and expansion tank starts to overflow once the water has got up to temp or once all the rads are hot. I've checked the ball valve and it isn't leaking. I'm hoping that a new thermostat will resolve the overflow issue. Any views on whether it will.
Thanks again.
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