Open system vent pipe horizontal run.

[Unklian]

Hi Again.

The problem.
Due to where stuff has been located for years......
Gravity hot water & pumped heating has been converted to
fully pumped. After a recent drain / inhibitor / refill, I just
can't seem to purge all the air from the DHW circuit.
(Pump fast / slow etc. can hear air bubbles & big chunks of air
running round the system but not escaping up the vent pipe.)
There are long horizontal runs in the loft, so (I'm thinking) any air which
is rising up with the flow, cant escape due to the long (12 feet) horizontal
pipe run in the loft.

Does anybody think re-routing the vent pipe much higher and
at about 45 degrees would help ? (The red dotted route).

Many thanks.

Ian.

 

[45yearsagasman]

Looking at your drawing, the only conclusion I come to is that if you have been converted to fully pumped then your vent and cold feed configuration is wrong.

 

[Unklian]

Yes, unfortunately, there are no dedicated fill / vent pipes
running through the house to the "correct" place. It would be a mammoth task.
I'm just trying to work out the best solution working with what I've got.

Ian.

 

[45yearsagasman]

View media item 32248
Ignore the reference to a back boiler, that is what you should try to achieve with a fully pumped conversion. Doesn't have to be 2 x 2 ports and can be one 3 port mid position. The feed and vent pipe connections are important for the system to work correctly.

 

[TicklyT]

From your sketch, it appears the only time that air can be released from the system is when hot water is selected on the programmer, and the cylinder is calling for heat.
At any other time, the motorised valve(s) will be closing off the primary circuit to both the cylinder and the open vent.

 

[45yearsagasman]

Which sketch are you referring to

 

[Unklian]

From your sketch, it appears the only time that air can be released from the system is when hot water is selected on the programmer, and the cylinder is calling for heat.
At any other time, the motorised valve(s) will be closing off the primary circuit to both the cylinder and the open vent.

Yes, that's correct.

Don't hit me, I didn't build the system but......

The pipework I have shown is the only fill / vent pipework.
I understand where it SHOULD go, but that would be a floors up / decorating job.
The Flow (& therefore the vent) pipework IS the first outlet from
the boiler in case of a runaway situation.
The DHW valve & Pump are both on the return side,
The CH valve is on the boiler Flow side, but AFTER a "T" where the DHW flow side is.

So......All the rads have bled nicely. CH is quiet.
When I start DHW, Cylinder calls for heat, valve opens, Pump / Boiler start. If you look again at my diagram, the boiler is another floor down,
under the header tank so, there is a long horizontal run of pumped / return heating water. This contains the air.
As the air bubbles get to the "T" , rather than rise up the short vertical bit
of pipe into the long horizontal run in the loft, they rush round the corner, round the heating coil.

I'm wondering if a possible help would be to (Temporarily) close down the output gate valve on the pump so that water (and air bubble) circulation is slowed to allow the air more time to rise up from the "T" ??
Once there is no air in the system, it runs fine. presumably, any tiny bubbles can slowly find their way out.

Any thoughts about losing the horizontal part of the vent pipe as suggested?

Would a more complete diagram help?

EDIT: Bit of history......It's a Glowworm Energy Saver, About 30 years old I believe. Made of about 5 components. It was converted to fully pumped about 5 years ago with an immediate 50% reduction in bills. You can imagine how innefficient the gravity hot water was with about 30 feet of horizontal pipe and about 5 feet of vertical. Boiler had to run at what felt like 400 degrees for water to circulate. There was no cylinder stat so baths were fun at about 20% hot tap, 80% cold. (Cold first to prevent scalding).

Ian.

 

[twgas]

You need to alter the pipework, as explained earlier, I suspect the problem is not the air wont dissipate but more is being sucked in when the HW is calling for heat.

 

[Unklian]

Where from though?
The only place it can "suck" from is the F/E tank.
It seems to be the same loop of water going round & round.
It contains air. There must be some method of allowing it to rise out of
the loop it's in.

Thanks very much for all the advice up to now.
As you've said & I know, It's plumbed wrong.
Thing is, Until I admitted this lump of air, it was working fine!
It's my fault and the Mrs. is making sure I know!

How's about cutting the 22mm "Hot side" pipe before
it enters the heating coil of the cylinder and "T"ing off a vent bottle?
That would be the highest part of the loop containing air.
The vent pipe would be out of the equation and only be used to allow
emergency venting in the event of a boiler "runaway".

Cheers.

Ian.

 

[compheat]

Cant you just move the F & E tank to above the vertical pipe runs from below.

Its the long horizontal cold feed thats the problem.

 

[matt1e]

Cant you just move the F & E tank to above the vertical pipe runs from below.

Its the long horizontal cold feed thats the problem.

Sounds like a plan!

 

[Unklian]

Possibly.

The airing cupboard is at one side of the house. (Right)
DHW big header tank is in the centre.
The CH header tank has been placed
at the opposite end of the house. (Left).
It would be very difficult to re-site it.
I presume that is why it is where it is.

I'm just wondering......You mention.......
Its the long horizontal cold feed thats the problem.
If the water can't get in fast enough, the air can't be pushed out?

AND......If that's the case......As well as a gate valve in the airing cupboard
alongside the cylinder, I don't know why AGAIN, but in the loft, half-way
along the horizontal "Fill" pipe, there is a 1/4 turn in line service valve?
I know these only have a bore of about 6mm.
Would that contribute to the problem? You can just see it at the bottom of the picture. (The vent pipe is now much taller, it used to just hook over the top of the tank under the insulation I fitted.)
looking at the picture, I wonder if the service valve was to
repair damage where the earthing straps are. Wonder if one was
tightened into the pipe?

Ian.

 

[mysteryman]

It would be a good compromise to convert this to a combined cold feed and vent, coming off the cylinder flow, and with as much slope as possible. This should not be the remote side of any motorised valves.

 

[twgas]

where's the vent pipe? if it tucked under the lagging it's not high enough, should be at least 450mm above water level.

 

[Unklian]

I've modified that now,
the vent does now come up at least 500mm above water level.

Tomorrow all being well, I'm going to remove the in-line isolating valve
and see if that has any effect.

If not, I might as a first attempt, build some kind of new mount to the right of the DHW header tank and fit a replacement F/E tank.
Perhaps one from Screwfix. The 4 gallon one.
Hopefully then, I'll have mainly vertical pipework.

Cheers.

Ian.