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Draining down a Combi boiler, any tips??....VENTED OR NOT???

Postby DUDE DIY » Tue Apr 15, 2008 5:48 am

Hi any advice is much appreciated. I have a Baxi 105 HE boiler and will shortly be needing to drain the central heating system down to reposition a few rad's as my kitchen is being extended. Ive taken a chance before and drained the system down and re filled on my own without problems before but, my questions are:

How do I know if I have a vented or unvented system?
Whats the difference?
Is there a difference when draining / re filling vented and unvented?
Is there any special precausions I should take or do?
Any additional advice?

Any advice, comments or pointers are greatly appreciated, last thing I want to do is cock my central heating system up.....the Mrs really would KILL me!

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Simply Build It

Postby htg engineer » Tue Apr 15, 2008 11:00 am

The Baxi 105HE is a fairly new boiler - so will be a pressurised system (sealed).

Draining down and refilling is easy, drain from a suitable point eg a drain off or a radiator valve.

Refilling, there'll be a filling loop on or near the boiler, will probably be a silver braided hose. This is how you refill the system - open the valve and pressurise to 1.0 - 1.5 bar, vent all radiators and keep filling until the radiators are full. When all radiators are full make sure the pressure is between 1.0 and 1.5 bar and turn boiler on - it may need repressurising and radiators venting again to allow any trapped air to escape.

There shouldn't be any problems with airlocks, if you find one or two radiators aren't heating - turn off the ones that are and it will push through.

Hope this helps
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Postby DUDE DIY » Wed Apr 16, 2008 4:33 pm

Great sound advice....much appreciated.
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