Simple explanations for plumbing problems

Filling loop left open

After use the valves on the filling loop should be closed, the metal braided filling loop removed and the valves capped.  The majority of people don’t do this so there is always a chance that the valves can be opened accidentally or be faulty.  This can allow too much pressure to develop in the system which may cause the metal pipe near the boiler to overflow.

The first step is to turn the taps so they are in the off position. If its a round tap turn it clockwise.  If it has a lever turn it so that is not in line and at 90 degrees with the body of the valve.  If it has been accidentally turned on you will hear the water flowing and hear the flow stop when you turn the valve to the correct position.

The filling loop below is open


The filling loop below is closed


It doesn’t need to be as pronounced as this to cause the pressure to go up, even slightly open is enough.

To fix this you need to turn both valves (or one if you only have one) off. This should make the metal pipe outside stop overflowing.

The metal overflow pipe should only overflow if the pressure is above 3. So when the pressure goes back down below 3 the water should stop.

If it doesn’t then you might need a new safety valve as they are notorious for not resealing after they have opened. This is a job for a gas safe engineer not DIY.

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When a leaking radiator drops pressure.

The pressure on the customers boiler had been gradually dropping over several months. As the drop was so slow it couldn’t be a massive leak. She showed me a radiator that had a rusty mark around one of the plugs at the top. This was more than likely the culprit.

Although there was no drip of water or any marks on the floor underneath it did feel wet to touch. Over several months this is enough to drop the pressure so it has to be changed.

The process of changing this plug is pretty simple. You can find a replacement plug on this link.

Turn off the valves, bleed the pressure out of the isolated radiator then take the plug out.

The valves were both lock shield types so I closed them with my tiny pump pliers.

Then I bled the excess pressure from the bleed point catching the dirty water in some blue roll.

When the water stops coming from the bleed point you can be pretty confident the pressure is gone.

Next unwind the plug from the radiator. I like to use pump pliers as they give a better grip. However they chew the fittings up. If they are on show or decorative you need to be more careful.

Some water will always leak out when you are repairing a leaking radiator. It's important to catch as much as possible.

Even though the pressure is gone a fair amount of water still comes out when the plug is removed. Have plenty of blue roll and a tray ready to catch it. I’ve got an old plastic tray that I’ve had for years but when it eventually gets broken I’ll replace it with a Plumb Tub to make life easier. Dirty central heating water can easily stain light coloured carpets make sure you have everything in place before you start.

Some water will always leak out when you are repairing a leaking radiator. It's important to catch as much as possible.

When the plug is removed clean the inside of the threads to remove any old sealant and dirt. Then refit the replacement plug. Use a flat spanner (I use an adjustable) to refit it. This saves the chrome from being chewed up.

Reopen the valves and check for leaks. If you have a pressurised system check the pressure gauge. Top up if necessary.

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