Combined Feed and Vent problems

[ClanMike]

I've checked all over this forum as there's a load of info here on issues with a combined feed and vent but I can't find an answer to my specific problem. I'm helping someone out with their new house where we've had to replace a couple of the radiator valves. Partly drained the system, replaced the valves and refilled. And then we found that the system has a combined feed and vent pipe to the header tank. Tried for days now to get all the air out the system but its still gurgling like a crazy thing - especially when it's just trying to heat the hot water. All rads are working fine apart from one that we drained plus another one. When we try to bleed them nothing comes out - even taken the whole bleed fitting out of the rad and still nothing comes out. There's just no pressure in the water to push the air out. And now we've found that the hot water is no longer heating up. I'm sure it's just air locks but we just can't get them out the system. Any advice would be great. cheers

 

[terryplumb]

Are there any air vents / air bleed valves on the pipework to the cylinder coil and if so have you vented there ?Have you checked / bled air from the pump ?

 

[OvertonPlumber]

Sounds like water starvation. Does the ballvalve run?
How has it been combined?
Does it have a high level inverted tee a horrible habit of british gas they block up.
You could reverse fill it of a hosepipe jubilee clipped onto a drainoff. Turn main on and slowly open drain off the main will then fill up the system

 

[ClanMike]

Thanks guys.
@terryplumb - There's no air vents in the system at all, apart from on the boiler. And yes, have bled the pump more times than I care to remember.
@MrBenchmark - yes, ball valve working fine. When I say it's been combined, I'm assuming that's the case as I can't find a separate vent pipe. There's a water feed from the expansion tank to the top of a T piece that's fitted to the top of the primary coil. What I don't understand is that the boiler flow appears to be connected to the bottom of the primary coil and the return is on the top of the coil, which is on the opposite side of the HW tank. I thought you always connected these things the other way round. I like the reverse fill up option. I'll give that a try.

 

[dilalio]

Your terminology is a bit confusing.
Photos would be helpful or a sketch.
Sounds like there is no vent pipe to the F&E at all!

 

[Nige F]

If you have the primary tappings top/bottom - opposite sides. It sounds like an old cylinder with a gravity circuit annulus inside it . It was common to convert these to pumped and flow in @ the bottom to chase the air out the top of the annulus. Rare to find one still in use now.

 

[ClanMike]

@dilalio - here's a sketch of the setup
@Nige F - is that the same as a Primatic system? If so, that would explain things as we can hear gurgling in the hot water tank. we were worried that the coil had ruptured inside. Also slightly worrying that the previous owners had been putting inhibitor in the header tank. So should we drain the system again and fill from scratch. Any advice on refilling? Why is nothing easy???

 

[Nige F]

No - not like a primatic. Completely separate waters. the idea of reverse pumping through is to reduce possible gurgling. Maybe turn pump down ?

 

[MeldrewsMate]

If the configuration you describe in your sketch is true then the air would automatically bleed via the filling pipe, but there are a couple of worrying aspects, especially as you have no open vent.
What size is the pipe feeding to the top of the cylinder coil? If 15mm it could easily block, if 22mm I have also seen them block, and this MAY explain why your system is failing to fill. The blockages are usually adjacent to the tee at the top of the cylinder. I suggest you partially drain down, cut the pipe at that point, and inspect for blockages.

@dilalioWhy is nothing easy???

As I often say to my customers when they say 'is that all it was?'.....'Just because I make it look easy doesn't mean that it is'

 

[ReganAndCarter]

As I often say to my customers when they say 'is that all it was?'.....'Just because I make it look easy doesn't mean that it is'

There's nothing to plumbing. All you have to remember is that hot water rises, and sh*t runs downhill.

 

[dilalio]

A strong Magnet might prove useful before you start cutting pipework willy-nilly!

 

[ClanMike]

thanks for everyone's help guys, I think we may be getting some where. we've had the pump turned down to lowest setting as it's only a single storey house. Is the gurgling a good or bad thing? If there is a blockage and we manage to clear it, will it still gurgle in the HW tank when we're refilling the system?

 

[Nige F]

Forgot to ask - what controls the heating/hot water ? Motorised valve/s.

 

[ClanMike]

@Nige F just one motorised valve, on the central heating loop. Nothing on the hot water loop. So what actually is the annulus and what is the gurgling sound in the hot water tank if it's two separate waters? Sorry, I'm just not understanding how the hot water tank works.

 

[Nige F]

If you google annulus you'll see the shape, it stands upright in the cylinder surrounded by the water that goes to your taps. The connections come out through the sides of the cylinder. It is as you know filled with the c/h water from the F+E cistern. The annulus was common for gravity ( thermosyphon) circuits before a coil was adopted. The top tapping is on the side a small distance from the top of the annulus so it traps a small bubble of air. No problem on a thermosyphon circuit but when pumped can cause some noise, as yours is.