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Central Heating

Drop in pressure in combi boiler 2 weeks after radiator removal and replacement


We've recently bought and moved into a house with a new valiant combi boiler which for the last 6 months (since we've moved in) has been absolutely fine. Over the last month or so we've had the upstairs renovated, and in doing so had a plumber remove 2 radiators from the wall for replastering, replace faulty valves, and then plumb them back on about 2 weeks ago. Absolutely no problems, and he checked for leaks at the time. This morning, there was a sudden drop in the boiler pressure which I rectified by filling the system. I want to know- is it possible that air in the system from the radiator works has caused this? Or is there definitely a leak somewhere?

2 Answers from MyBuilder Heating Engineers


It is possible it is just air in the system from the works carried out. It has most likely found its way out via the auto air vents in the boiler. Just keep an eye on it over the next couple of weeks/months and keep a log book of how often you are filling up to assist the engineer if he has to return

Hope this helps


Answered 24th Apr 2015

Most likely cause, as above, air has been expelled via the auto air vent !

There is the air that is displaced when you re fill the system & ' vent the radiators '

Then by nature water, ( H2O ), has an air content !

(This is compressed / released when the water is heated ),
After commissioning the new radiators, the system should be run at full temperature for as long as you can stand it !

Finally there is the gas created from the reaction between the different metals in the system. Typically copper and iron which react to form ferric oxide, which also vents out of the system !

My advice would be to make sure the system is dosed with an inhibitor chemical, and fit a magnetic filter to the system !


Answered 1st May 2015

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