Leaking overflow & high pressure from combi boiler

wadeo0

Hello,
Recently noticed our boiler's overflow pipe running a river down the side of the house. Looked at the boiler and the pressure is high (about 3.5). Have tried a letting water out of the system by radiator bleeding but didn't seem to have any effect. Took the front off the boiler to try the pressure release valve - when turned pressure goes down but instantly shoots back up. There is also what looks like a small leak (and some rusting) around the bottom of the valve piping where it joins the chassis of the boiler. Other things I noticed are when taps are running pressure goes down to around 2.5ish, but goes back up when tap is turned off, can also hear a sound when I put my ear to the boiler - almost a hissing which sounds like water running through the system. Boiler is Vokera Compact 24.

I have very limited knowledge of this stuff but from reading up online it sounds like there could potentially be a leak that is allowing mains water into the system (would explain why pressure goes down when taps are on) and increasing pressure - would this come from a faulty heat exchanger? Any other ideas of what could be causing it? Hopefully moving out soon so hoping it isn't too much of a pricey one to fix!! Currently got a hose attached to overflow outside running into a drain so it doesn't flood the patio but will call plumber tomorrow, just wondering if anyone on idea has any other ideas.

Cheers in advance for any info!

jefaz07

On the right hand side is there a lever the wrong way? Or a separate full loop. Sounds like it’s permanently open

jefaz07

A pin holed plate to plate wouldn’t normally fill up so fast. Isolate main to boiler and open hot tap...does heating water come back the other way?

wadeo0

jefaz07 wrote: »

On the right hand side is there a lever the wrong way? Or a separate full loop. Sounds like it’s permanently open

The filler loop switch is definitely in the off position. I also disconnected the filler loop hose and that had no effect on pressure.

jefaz07

Isolate cold feed into the boiler on the right. Take some pressure out...is it still happening?

wadeo0

jefaz07 wrote: »

Isolate cold feed into the boiler on the right. Take some pressure out...is it still happening?

Isolated boiler from the mains and released pressure.Was back in the red after a few seconds. Seems the only reliable way to reduce pressure is by running the tap...I can get it down really low by leaving the tap on for a while (and this also makes the outside leak stop), but as soon as I turn it back off the pressure dial ticks back up and leak starts again!