Low mains water pressure - found leak at outdoor oil boiler??

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I'll be trying to get onto a plumber tomorrow morning but in the mean time I'm interested in people's thoughts here.

Symptoms from yesterday:

Low mains water pressure to all cold water taps

Central heating only getting the radiators luke warm

Burner firing continuously for the timed periods

Today removed the back panel of the Grant Vortex and heard what sounded like a leak from the flow/ return pipes in the ground under the boiler. I could also see some water bubbling.

I turned off the mains on the road and the noise and bubbling stopped.

Turned the mains on and it returned.

Can anyone suggest what may be happening here?

I've turned all heating off until rectified.

Wearb

Is it a fairly new install?

Sound like a joiner after failing. You won't know for sure until you expose the leak. Check where the other ends of the pipes appear in the hot press, in case its a leak from there and following the pipework to the boiler. You should be able to isolate the boiler and turn the mains back on.

Is it a sealed system?

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It's a sealed system installed about 4 years ago.

The hot press shows no sign of leaks although some copper pipes have condensation which I haven't seen before.

Picture below shows the flow return pipes at the external boiler (~10m from hot press) I can see water bubbling about 4/5 inches below the surface so I'm assuming there is a leak close to this?

Am I right in saying that mains water in my case is replacing the old style tank in the attic for system top up? And now I have a leak in the primary sealed system so the mains is constantly trying to top the system up?

Wearb

Yes. But the mains shouldn't be topping it up. There must be a valve left turned on somewhere in the hot press.

Also because the boiler continued to run, it's likely that the leak is on the pipe supplying water to the boiler. The valve for closing it is likely on the pipe showing condensation.

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Thank you! I followed the condensing pipe in the hot press and there was a valve 'on' when I turned to off the mains pressure is back to normal.

I'm guessing I still have a leak somewhere in the pipe near the boiler?

Wearb

Yes. You've likely just isolated the supply to the leaking pipe.

At least you'll have water for the house now.