Combi Boiler.. Under pressure!

22 Feb 2016
Reaction score
United Kingdom
Hi all!

I live in a flat on the first floor of a converted house.

About six months ago i had a combi boiler installed to replace an old failing boiler. Recently the boiler will occasionally fail to fire up to due to the pressure dropping to 0.. This normally happens if I am away for a night or two and so the boiler doesnt get fired up for any reason.

Now what has happened more recently is if the pressure is below 1 bar it fails (as expected) so the plumber told me to locate the filling loop and give it a quick turn to "top up" the pressure and as expected, it works.

However lately the pressure has occasionnaly crept up to 3 bar and the overflow pipe is leaking/dripping constantly much to the rightful annoyance of my downstairs neighbours.

I can temporarily rectify this by turning off the boiler and bleeding the radiators in the flat. This drops the pressure of course. And all is well temporarily. However I am now worried whenever I need to actually use the boiler and call for hot water, it will force the pressure back up again? (Ie causing me to have to bleed rads to relieve, so I can stop the overflow dripping constantly!)

I have had a look an i can see when i turn the little valve i use to top up the pressure (and clearly water flows the second I turn the value in line with the pipe) and it appears this is the filling loop.. It is a sort of shiny metal rope part, for want of a better word!

If anyone could give me any insight, much appreciated!

I am a lamen but if i had to guess I believe that perhaps the boiler pressure rises beccause somehow water is slowly getting in via the filling loop, even though the valve (i can only see one valve?) is across the pipe and i cannot hear any water flowing.
ALSO: The is a tap/valve right next to the boiler pressure meter (see pic), when i turn the valve (any way at all) nothing happens?! Should this not drain pressure/water?

For reference:
The boiler has a MagnaClean fitted.
There are a few visible stain marks on the MagnaClean and below.
I have posted some pics for reference.

Very much appreciated!


MagnaClean with some visible stains?

Overflow to outside wall


(ABOVE) Valve i turn to top up boiler if needed


(above) This is the boiler pressure meter, important, when i turn the valve, nothing happens?! Should this not drain pressure/water?


(above) Boiler model
Last edited:
Sponsored Links
Two things to check.

1. Disconnect the silver rope thing. Filling loop. This will show you if a valve is passing either by water showing up or pressure stopping to rise.

2. Expansion vessel pressure needs checking to see if that is the cause of the issue.

After that let us know what you get and we could help further.

Thanks Jon.. Any advice on removing the filling loop? Should i turn the water off at the stop-cock?
Sponsored Links
OP There's no need to turn off the main stop cock. If it was passing that much trust me you'd know.

On either end of the filling loop will be a valve and a butterfly style nut. You can see one in your picture. Ensure that the valves are turned off properly and then undo the butterfly style connection.

The braided hose can then be removed. You will get a little water out initially as it will be sitting in the pipe so that's nothing to worry about. If the mains side of the valve continues to drip though then you have a problem. Get the hose out first and you will need to take it from there.


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local