help please - boiler pressure rising high when central heating turned on

[oje29383]

Hi everyone I'm having issues with my combi boiler. When the central heating is turned on the pressure keeps rising to 3.7+, when the hot water on it rises to around 2.1 and when it's not heating the pressure is around 1.5 bar.

There is a filling loop that's detatched but I can't find where it should be attached to. Also is this silver part an auto fill valve or what is it? The two valves that regulate it are in the open position. Have tried bleeding the radiators but the pressure still increases very high when the central heating is turned on, is this to do with this auto fill loop/valve?

How to stop the pressure getting to high?
Any advice would be appreciated thank you!

View attachment 359735

 

[Johntheo5]

It looks like a auto fill, if the pipe from the right is from the cold mains to the combi and the left pipe goes to the combi flow or return pipes then it is. however, since the pressure falls to 1.5bar then it may not be a problem. It looks like the boiler EV (expansion vessel) has lost most of its precharge pressure but can still deal with the small vol of heated primary water circulating with HW demand but cant handle the system contents expansion with CH on, so EV requires checking and its precharged pressure restored to probably 1.0bar. Also the pressure should not rise to 3.7bar because the boiler pressure relief valve should lift at 3.0 bar, on some boilers you can observe this coming from a small pipe that exits from the wall behind the boiler to the outside, others might go to the boiler condensate drain so more difficult to see it.

The boiler itself should have a pressure gauge, what does this read?

 

[RandomGrinch]

It looks like a auto fill

I thought it looked more like a pressure reducing valve on the incoming mains supply - especially given the maximum guage pressure?

 

[oje29383]

Thanks so much for your replies! So what the gauge is set to is ok (red / black)?

I didn't observe any pressure relief valve lifting, the pressure just keeps rising.

Is the EV affected by the boiler being off? When I moved in the boiler was off - maybe for a long time? I'm not sure. Would turning on/off the boiler without the thermostat manually affect the EV? Is there a way to stop the EV losing it's precharge pressure?

 

[Johntheo5]

Yes with that big bore pipework looks as if it could be but why does it settle to 1.5bar?

 

[Johntheo5]

Thanks so much for your replies! So what the gauge is set to is ok (red / black)?

I didn't observe any pressure relief valve lifting, the pressure just keeps rising.

Is the EV affected by the boiler being off? When I moved in the boiler was off - maybe for a long time? I'm not sure. Would turning on/off the boiler without the thermostat manually affect the EV? Is there a way to stop the EV losing it's precharge pressure?

First try and establish exactly what that PG is reading, if the PRV is between the mains and the boiler flow or treturn the it is a auto fill, if not, then as suggested above its on the cold feed to the boiler, does the boiler have a PG??

 

[oje29383]

It's a vaillant, there's a digital screen that shows the pressure which is what I observe increasing and it doesn't match that gauge in the picture that doesn't change

 

[Johntheo5]

You will have to get a gas resistered person to check maybe first that there is no blockage in the pipe supplying the digital PG, if no problem, then the EV and the pressure relief valve, if the PG is correct then a new pressure relief valve should be installed.

 

[oje29383]

Ok thanks for your help!

 

[gas112]

pressure rising with heating on the expansion vessel in the boiler has lost its charge and needs re pressurizing

 

[Madrab]

As everyone has said - get an engineer in and get them check the expansion vessel, that'll be why the boiler pressure rises.

The concern is though - that pressure reducing valve fitted on the cold feed, the big silver and black valve with the gauge. That is sometime fitted as a bodge to keep the system topped up if there is a leak, as @Johntheo5 mentions, an autofill - and that keeps the system @ a constant 1.5bar.

Can you give us a couple of pics at a higher angle looking down on all the pipework? Especially where that copper pipe out of the gauged black/silver valve heads back into the thinner silver valve and where that then connects to.