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Who's right ? (Read 3730 times)
thescruff
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Re: Who's right ?
Reply #29 - Jan 13th, 2018, 10:58pm
 
Image 4   

A little fag package sketch I knocked out for you.

Cold feed and vent should be as close as possible. When the pump starts and shortfall should take water from the cold feed and NOT the vent, doing the later highlights a problem, normally a blocked or semi-blocked cold feed.
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thescruff
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Re: Who's right ?
Reply #28 - Jan 13th, 2018, 10:30pm
 
Sort of, you have a problem with air in the system, now you know where it's coming from.

Maybe the pump is at the wrong speed, the connections are wrong, the tank and or vent is too low, but that should make any difference if the neutral point is correct.

To comment further one needs information, and preferably a good as fitted drawing, or seeing the job which is unlikely.

If it wasn't new one would say the cold feed is blocked.
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Re: Who's right ?
Reply #27 - Jan 13th, 2018, 10:22pm
 
thescruff wrote on Jan 13th, 2018, 10:16pm:
Separate post to avoid confusion.

......
The bubbles when the pump stops is because the pump is sucking air in when it's running


Can you please clarify this one for me as I'm struggling to understand this.  Are you saying that there is constant air being drawn into the system and escaping via the vent pipe while the pump is running ?
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thescruff
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Re: Who's right ?
Reply #26 - Jan 13th, 2018, 10:16pm
 
Separate post to avoid confusion.

A heating pump doesn't pump, it circulates at a high velocity, You would find near as a 1bar pressure differential across the inlet and outlet of the pump.

The bubbles when the pump stops is because the pump is sucking air in when it's running
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thescruff
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Re: Who's right ?
Reply #25 - Jan 13th, 2018, 10:06pm
 
No gold star only for effort and finding a problem.

The neutral point isn't neutral as nothing should happen.

The Plumber needs to come back and sort it.

If the engineer wants help get him to improve on the sketch.
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Re: Who's right ?
Reply #24 - Jan 13th, 2018, 11:46am
 
thescruff wrote on Jan 9th, 2018, 1:24am:
Back too one of my earlier post.

You have a header tank for the heating, hold a jar of water under the vent, turn the pump on and off a few times, does it drink the water or blow bubbles.

Can you post a pic of the neutral point.



OK.

Switch the pump off and air bubbles come out.

Pump back on and the water gets sucked into the vent pipe.

I'm not sure what I was expecting....part of me was thinking nothing hence the 'neutral point'.

EDIT:  OK, think I understand what's happening and it is as expected.  We've got a body of water circulating by virtue of the pump running. When the pump stops, the momentum of that water pushed up the vent pipe a bit ...pushing out air in the downspout of the vent pipe (the bit hanging over the header tank).

When the pump starts up again there is a momentary low pressure at the neutral point as the pump starts sucking and the inertia of the water in the CH circuit takes a tad to get moving again.  So that sucks water into the vent pipe.

Ergo the pump is running the right way round.

Do I get a gold star ? Grin
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thescruff
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Re: Who's right ?
Reply #23 - Jan 12th, 2018, 12:29pm
 
give or take 2-3 weeks all the air should be out unless you have a system fault, which is why I'd like you to check the header tank as per my earlier posts.
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londonman
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Re: Who's right ?
Reply #22 - Jan 11th, 2018, 1:00pm
 
thescruff wrote on Jan 10th, 2018, 8:46pm:
If the air gets to the rads then it is likely to collect the air and you may find one rad collects more than the others. that is normal although once the air is out it should stay out.

Have you got an inhibitor in the system.


Yes I do but given the amount of bleeding I will be topping it up.
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thescruff
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Re: Who's right ?
Reply #21 - Jan 10th, 2018, 8:46pm
 
If the air gets to the rads then it is likely to collect the air and you may find one rad collects more than the others. that is normal although once the air is out it should stay out.

Have you got an inhibitor in the system.
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londonman
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Re: Who's right ?
Reply #20 - Jan 9th, 2018, 9:08pm
 
Mmm...intriguing.  Thing is the rad that I bleed to fix the problem is the one furthest away from the pump ie 'downhill'.
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thescruff
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Re: Who's right ?
Reply #19 - Jan 9th, 2018, 6:47pm
 
where the pipes rise there should be air vents to take the air out at high levels.

You'd need to see it to decide where is best.
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londonman
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Re: Who's right ?
Reply #18 - Jan 9th, 2018, 4:33pm
 
Yes, I thought so to.

On another forum I was asked some very cogent questions,  and some that I couldn't answer.  For example, why would air 'block' the flow ?  So I did a bit of Googling to find out why and came across this...

In a well designed low pressure water pipe system, air should clear naturally even if you run out of water. As the pipe system fills again, the air should naturally rise to the top and be expelled. Air locks happen when the pipe system is not well designed.

Air bubbles rise to the top because air is much lighter than water. In a correctly installed low pressure pipe there is a natural "fall" towards the taps. Friction between the water and the pipe walls provides a resistance to the flow. The fall in the pipe is needed to overcome the resistance.

If the fall in the pipe is continuous, any trapped air going the other way in the pipe will be following a natural rise. Given a little time it should bubble back into the cold tank or, if it's a hot water pipe, bubble back towards the cylinder and up the open vent over the cold tank.

Resistance increases with the length of the pipe and long horizontal sections can be a problem because they have no fall.  Short horizontal sections of pipe are not normally a problem.


And therein lies the problem, I think.  There are two pairs of 22mm pipes that run 'horizontally' down the length of the house.  One pair were the flow and return for the radiators and the other air the flow and return to the HW cylinder.  I don't recall exactly but I have a vague recollection that they may well have risen slightly from the old pump end.

Now with the new modified layout we have a bit of a rollercoaster.  I wonder if this is the cause ?

...

Having aid that the cure has always been to bleed the return side of things and we've not touched that but the fact remains that for part of the radiator circuit the flow is in the opposite direction to what it was and most likely downhill.

The article then goes on...although I admit I don't follow it 100%

Pipes which rise towards the taps are a big problem. However, we can ignore the last short section of pipe connecting to the tap which nearly always rises vertically. Any air going to the top of that section is simply passed out through the tap. If a low pressure pipe rises on its way towards the taps, any air going the other way would have to go downhill. Because air is lighter than water it gets trapped at the top of the rise in the pipe. This air pocket adds a lot of resistance to the flow of water. If there is not sufficient overall fall along the length of the pipe to overcome that extra resistance, the pipe becomes air locked.
When an air lock forms, the flow of water from the taps may reduce dramatically and can sometimes stop completely. If the air lock is in a cold supply pipe it may also stop the loo filling.
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thescruff
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Re: Who's right ?
Reply #17 - Jan 9th, 2018, 12:41pm
 
That looks 1st class, one should assume he knows what he's doing.

Ask the guy where the air is coming from and what he can do. Most of the air should be out by now.

Check the header tank when the heating is on, is the ball valve dribbling or pumping over the vent.
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Re: Who's right ?
Reply #16 - Jan 9th, 2018, 10:33am
 
Many thanks for your continued support, Scruff.

Here is a photo of the neutral point - located upstairs landing

...

Be a while before I can get help to turn the pump on/off while I am up in the loft
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thescruff
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Re: Who's right ?
Reply #15 - Jan 9th, 2018, 1:24am
 
Back too one of my earlier post.

You have a header tank for the heating, hold a jar of water under the vent, turn the pump on and off a few times, does it drink the water or blow bubbles.

Can you post a pic of the neutral point.
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londonman
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Re: Who's right ?
Reply #14 - Jan 8th, 2018, 9:58pm
 
CWatters wrote on Jan 8th, 2018, 4:49pm:
I'm late to the party but it seems odd to me to have a heat store heating a hot water cylinder. Normally you would just have a coil in or heat exchanger on the heat store to heat DHW.





Red herring.  Don;t go there.
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londonman
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Re: Who's right ?
Reply #13 - Jan 8th, 2018, 9:57pm
 
thescruff wrote on Jan 7th, 2018, 9:18pm:
In your 2nd drawing you show a red pipe heading back to the store and a pink pipe going I assume the heating.

Where it has been modified the pump looks to connect to the red pipe.

Is the red pipe now the flow and where does each end go.

What happened to the pink pipe and where did it go.



I see the confusion. My bad. Sorry.

Ok..in the original system the hot water from the store split into the two circuits  - HW and CH.  In drawing two, that red arrow going approx 10 o'clock is left over and should not be in the drawing.  The plumber has used what was the original feed pipe to the HW cylinder as the pipe to get the hot water from the store and into the house where the new pump is located...just to get his bloody neutral point and to keep him happy.

So at the end of that pink pipe he's broken it away from where it was feeding the hot water cylinder and it now goes to the pump at its new location.  After the pump the usual two motorised valves are there ....splitting the hot water flow to the HW cylinder and radiators.   The new connection to the radiator circuit is that grey pipe. So the hot water now injects back into what was the CH main flow pipe.

I can't recall how the original two returns came back together prior to returning to the heat store.  Now hidden behind plaster.
I'm now not bothered about the heat loss as I'd like to stop the bloody thing from stopping working.

Turned the pump off to do some work.  After switching it back on...no heat downstairs and upstairs rads lukewarm.  Fiddled about with a hose pipe in the bleed valve orifice and finally got the system up and running again.

Now today, I put on the TRVs which had the effect of turning the pump off ...as it were...as the sodding system has stopped heating again.  Tried the hosepipe bleed this evening but failed miserably.  There is an airlock keeps getting introduced into the return pipe(s) somehow.

Am I allowed to say I hate this f***ing system ?
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