Can't find filling loop

bren2001

Boiler has low pressure. I've no idea how to top it up. It's a Logic 18IE. I can't see any filling loop.

stephenmarr

That 1/2 Gate valve top picture.

bren2001

https://www.boards.ie/discussion/comment/124005010#Comment_124005010

I thought that myself. Opened it, nothing happened. I'm assuming I'm missing something incredibly obvious here?

10-10-20

WWhat Pressure does it normally sit at? And try tapping the one-way valve below the gate valve with a stout screwdriver or light hammer.

bren2001

https://www.boards.ie/discussion/comment/124005540#Comment_124005540

It's currently sitting at around 0.5/0.6 bar.

The pipe with the 1/2 gate valve runs to the tank in the attic. I think the valve is simply to cut off water to the hot water tank if needed. There's an old feed and expansion tank in the attic which, I assume, is from the old system as the Logic 18IE is a sealed system.

I'll try tapping the pipe alright but I don't think its the filling loop (I also have zero idea what I am talking about!)

10-10-20

https://www.boards.ie/discussion/comment/124005844#Comment_124005844

If you trace it down you can see that it's connecting into the bottom of the cylinder, part of the heating coil in the tank. So would seem to be the filling loop alright. If it's coming off the attic tank which is around 2m above the system then the max system pressure would be around 0.2 bar. I think that's called a low-pressure sealed system. So that's why I asked about the normal pressure of the system as it might not ever be expected to be above that value.

bren2001

The blue line connecting to the 1/2 gate valve runs to the bottom of the tank. (i assume is just fills it up?). The red line is the coil return. The pipe from the attic (blue line) runs behind the yellow box and doesn't connect to it in any way. I don't see where the coil return and the supply from the tank interact.

The documentation for the boiler indicates the minimum operating pressure is 0.3 bar so I don't think it is a low-pressure sealed system.

Apologies if I am being dumb here, I'm just trying to top up my boiler

RebelButtMunch

Did you try open that red valve and listen to hear if it fills?

10-10-20

https://www.boards.ie/discussion/comment/124006040#Comment_124006040

The blue line is the coil feed, red is coil return (or can be the other way around in reality). The tank feed (replenishment) is elsewhere, usually at the rear. Just fire up the boiler to heat the tank so we are all agreed.

bren2001

https://www.boards.ie/discussion/comment/124006078#Comment_124006078

Ah! That makes sense.

When I fire up the boiler both the coil feed and the return should be hot? (obviously at the point of entry/exit not near the red valve).

https://www.boards.ie/discussion/comment/124006056#Comment_124006056

Yeah but nothing happened. There's a second red valve in the attic which is also connected to this pipe so I might just need to figure out if 1 is open and the other is closed etc.

Lenar3556

https://www.boards.ie/discussion/comment/124005896#Comment_124005896

Yes - more commonly called semi-sealed. It would never have been at any more than 0.2-0.5 bar.

You will see a non return valve which in theory stops water going back into the cold water tank when the system heats up.

Not a great job. But I wouldn’t be converting it to fully sealed unless I had to. The higher pressure can often expose leaks in older systems.

10-10-20

https://www.boards.ie/discussion/comment/124006321#Comment_124006321

I converted my semi-sealed over to fully-sealed 2 years ago having eliminated all leaks before that. I put a pressure sender onto it so that I can get notified if the pressure drops below 1bar. So far I only topped up to 1.5bar in Feb, so delighted with the lack of leaks since.

10-10-20

https://www.boards.ie/discussion/comment/124006094#Comment_124006094

Coil feed will be hot and return will be warm to hot. yep.

Lenar3556

https://www.boards.ie/discussion/comment/124006954#Comment_124006954

very good. What are you using to monitor the pressure?

10-10-20

https://www.boards.ie/discussion/comment/124006966#Comment_124006966

It's not an off-the-shelf solution unfortunately - it's Home Assistant with a pressure transducer connected into the ADC ports of a little WiFi/microcomputer board (ESP32).

DublinDilbert

No return valve might be stuck, give it a few taps and open the bleeder

bren2001

https://www.boards.ie/discussion/comment/124006957#Comment_124006957

You’re certainly correct, both hot so it’s the feed and return.

I tracked the blue line in the attic, runs to the feed and expansion tank/ header tank. I assume then the red valve is to shut off this tank if needed and there is no filling loop. It’s an unsealed system (or semi sealed)?

Not sure how I do get a pressure of 0.5/0.6 bar with that setup but….

John.G

In a semi sealed system, the boiler pressure gauge (if installed) will read, when cold, the height/head of water from the water level in the feed&expansion cistern to the boiler, if this height is say 3.5M then the pressure gauge will read, 3.5/10, 0.35bar, this pressure will always be 0.35bar every time the system cools down. When the boiler and system, rads etc heat up, this pressure, due to the expanded hot water will rise to a pressure determined by the average system temperature, the system contents and the size of the EV (expansion vessel) and its (air end) prepressure, this also assumes that the non return valve is tight and not allowing the expanded water back into the feed&expansion cistern.

Assuming a 10L EV, pre pressurized to 0.35bar, system contents of 85L, and the average hot water temp at 60C, then the boiler pressure should read 0.57bar(hot), if the EV prepressure is 0.5bar then the hot pressure will be 0.75bar. If the pressure doesn't change between hot and cold conditions then the NRV is leaking past and the ~ 1.4L of expanded hot water is just returning to the feed&expansion cistern, the pipe (if the NRV leaking) should feel hot/lukewarm and the cistern level, depending on its volume will rise and fall by say around 10mm or so.

IF semisealed, the supply ("filling loop") to the boiler must always be left open.

bren2001

https://www.boards.ie/discussion/comment/124008067#Comment_124008067

Ah yeah, I understand the physics behind it. The tank isn’t anywhere near 5/6m above the upstairs pipes so how it sits at 0.5 bar is beyond me.

John.G

The NRV (opposite the isolation switch) with its arrow pointing downwards would seem to indicate a semi sealed system but if the pipe its installed on is from the feed&expansion cistern then, as you say, the (cold) pressure can't be 0.5/0.6bar, but it can if that filling pipe is from the mains or if there is another filling loop somewhere else. You said in your first post that the boiler has low pressure, does it still have low pressure at 0.5/0.6bar or was it lower when it had low pressure, is the boiler firing up now?, if so then that pressure has to rise and fall except the pressure gauge is reading high or stuck and the NRV is leaking the expansion back up to the F&E cistern (if this pipe is from there).

Where is the expansion vessel located and where is the pressure gauge?.

Damien360

That's similar to my one. The loop fill is that qualplex line coming down from the valve going to the bottom of the cylinder. Check the joint between the qualplex and the copper. I'd bet there is a small on/off screwdriver type valve on that. It can be a pig to get it absolutely level after. Might be just unsighted from you.

Mine has that valve above the braided tubing and follows down through a manual pressure gauge to base of cylinder which is where they all fill.

bren2001

https://www.boards.ie/discussion/comment/124008483#Comment_124008483

Pressure is 0.5 when cold and >1.0 when hot. It doesn’t get lower than 0.5.

Expansion tank in the attic, pressure gauge on the boiler on ground floor. So there would be 5m to the tank in the attic. So the pressure does make sense, not sure why I didn’t cop that yesterday. I was only considering the height between the expansion tank and my hot press.

John.G

If you mean the OPs, then that looks like a non return valve to me with the arrow pointing downwards, between the copper and the qualpex?

John.G

https://www.boards.ie/discussion/comment/124008597#Comment_124008597

So, every thing fine now?, you have a semi sealed system with the expansion vessel (& pressure gauge) in the boiler, problem was isolating gate valve was closed?.

bren2001

https://www.boards.ie/discussion/comment/124008662#Comment_124008662

Yeah, it’s all fine. Thank you all for the help!