Icon 23t Banging

15 Jul 2004
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United Kingdom
I have just moved house, and have a Icon 23t Combi boiler installed. The problem is that the two red central heating valves are closed, as the weather now is getting a bit cooler I want to put the central heating on. Once I try and open the central heating valves all you can hear is water trying to enter the pipes and a loud banging noise, meanwhile the pressure dial on the boiler fluctuates wildly between 2 and 4 bar for 20-30secs and then settles at 3 bar. The boiler seems to let out / drip waters out though a pipe to outside (I take it this is a pressure release system?). The hot water is fine, but I can’t find any indication that the boiler has been serviced since 2001.

Do you have any ideas? I hope that all is needed is a service??
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What seems to have happened is that the boiler isolators (the red valves) have been closed for some reason (they should NOT be closed) and the system filling loop is 'open' - ie. the valves that let water from the mains into the rads, etc., are open. So your rads and pipes are all sitting at mains pressure - a Very Bad Thing!

First step: turn off both valves on the filling loop (the silver-coloured flexible pipe somewhere below the boiler).

Then bleed any air out of all the rads, starting at the lowest. When you get to the highest one, let air AND water run out of the bleed valve until it stops flowing of its own accord.

Then, having made sure all the bleed screws are tight and with the boiler OFF, slowly open both red valves under the boiler. Pressure may go to down to between 0 and 1. If so, crack open the filling loop valves to bring the pressure back to 1 Bar or so, then CLOSE BOTH VALVES. See if boiler works.

Otherwise, if pressure still well above 1, let some more water out of the bleed screw of a radiator until the pressure gets to one. Test boiler.

Find out who turned off the isolators on the boiler in the first place and make sure you handcuff them whenever they come to visit!
It COULD be that the "Two red valves" ARE the filling loop valves. You would get a noise of water and rising pressure and a leak from the pipe through the wall!

yj6aa - stop playing, put those valves back where you found them. Call an engineer before you do more damage.
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Thanks for the reply and help. Will keep anyone away from the boiler unless they are an engineer!!

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