Boiler pressure dropping

ValiantUK91 · 2 Feb 2019 at 14:51

Just got back home to find out I've got no hot water, I checked the boiler (ariston microcombi 23 mffi) and the pressure is on zero so I open the inlet valve allow it to fill back up to 1 bar of pressure but as soon as I close it the pressure slowly drops back to zero.

I've been around the house now 3 times checking all the radiators and pipes that I can see for leaks checked the ceilings for any damp patches but not seeing anything at the moment. The radiators were full of air so bled them til air stopped coming out but no water followed so back to the inlet again and topped the pressure back up to 1 bar and it stayed there until I put the hot water on and it went back to zero again.

Any ideas on what could be the issue?

Cheers

sja360 · 2 Feb 2019 at 15:08

Was the boiler running when you left ? It could be the overpressure valve has opened and dumped the system water into an outside drain? Maybe that valve is faulty.

ValiantUK91 · 2 Feb 2019 at 15:13

No the boiler was off when I left this morning and the heating only comes on when I turn it on so it wouldn't of come on at any point while I was out

Jokester · 2 Feb 2019 at 15:14

My money would be on the PSV as well being stuck open or leaking.

How quickly is the pressure dropping?

ValiantUK91 · 2 Feb 2019 at 15:15

Just noticed the pipe that goes out of the wall and into the drain outside is dripping water after putting the pressure back up to 1bar again

ValiantUK91 · 2 Feb 2019 at 15:20

Jokester said:
My money would be on the PSV as well being stuck open or leaking.

How quickly is the pressure dropping?

Straight away like I stated pretty much at the same time you posted that pipe is drippi g which I believe is the pressure relief pipe

JasonM · 2 Feb 2019 at 16:11

Are you getting high pressure when radiators warming, then low pressure after system shuts down. If so it could be an issue with the expansion vessel, if this is not working correct, system pressure will go very high, the pressure relive valve will activate, then once the heating has shut down the pressure will go very low or even zero.

If it is expansion vessel it could just need servicing and water pumping from it.

ValiantUK91 said:
Just got back home to find out I've got no hot water

Just read this top line, this makes no sense as hot water not effected by pressure, pressure is your system pressure. Is the boiler not operating at all when you turn hot taps on?

ValiantUK91 · 2 Feb 2019 at 16:29

Boiler doesn't operate when hot taps are turned on unless I put the pressure up to around 1.5 bars then the boiler kicks in but then it slowly looses pressure and cuts off. I've just gone to test this again and it did exactly that it's now down to 0.5 bars the boiler kicked in for a moment when I turned the taps on with that pressure then it cut out and pressure dropped to 0

darael · 2 Feb 2019 at 16:54

I am also betting it's the expansion vessel. When I had problems with mine on my old boiler, I think it spat out some water from the pressure relief pipe too. This might have happened to you, but sometimes the seal on the valve doesn't seal properly again afterwards. At least that's how I recall my plumber describing to me. One new expansion vessel and PRV and the issue was sorted.

£15 · 2 Feb 2019 at 21:50

Once the PRV has opened it frequently gets clogged with debris contained in the escaping water and 'sticks' open. As it's still allowing water to escape it sounds like it's going to need replacing.

You then need to investigate why it activated in the first place. Again, a frequent cause is the expansion vessel.

I've had these issues with my last three boilers.

So what the others have said.

xb8browney · 2 Feb 2019 at 21:53

Sounds like expansion vessel to me.

Saytan · 3 Feb 2019 at 09:53

Just had my expansion vessel replaced to solve a similar problem on my vaillant boiler

ValiantUK91 · 3 Feb 2019 at 18:14

Cheers for the responses guys, got in touch with 3 plumbers today about the issue one was too busy due to a lot of calls in the past few days the other 2 both stated it could be the cold weather causing my pressure to drop due to expanding pipes I tried explaining my issues and what was going on but they just seemed like they didn't want the work. Is that possible regarding expanding pipes causing loss of pressure? After what you lot have said and some research on the Internet it does seem to be either the pressure release valve or expansion vessel.

Going to try a ring around again tomorrow to try and get someone out to have a look.