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Who's right ? (Read 605 times)
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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londonman
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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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Re: Who's right ?
Reply #12 - 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.



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Re: Who's right ?
Reply #11 - 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.
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londonman
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Re: Who's right ?
Reply #10 - Jan 7th, 2018, 9:16am
 
thescruff wrote on Jan 6th, 2018, 8:59pm:
Yes I know that but the store return and heating return have to be at least common somewhere in the circuit


Not sure what you mean by the 'store return'.  I have two separate heat exchanger coils inside the heat store.  One of them comes from the oil boiler which heats up the water.  The other feeds the ch/hw circuit
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Re: Who's right ?
Reply #9 - Jan 6th, 2018, 9:03pm
 
Can you pencil a sketch and add flow arrows and id the pipes
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Re: Who's right ?
Reply #8 - Jan 6th, 2018, 8:59pm
 
Yes I know that but the store return and heating return have to be at least common somewhere in the circuit
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Re: Who's right ?
Reply #7 - Jan 6th, 2018, 4:53pm
 
The heat store is the only way back.  Just think of it as a central heating boiler.
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Re: Who's right ?
Reply #6 - Jan 6th, 2018, 10:15am
 
Yes, I realise that, but it looks like the store circuit is the easy way back.

It had an MV before so there was some control on it and assume that is still the case, but is there a valve on the return you can adjust, To balance the circuit a bit
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Re: Who's right ?
Reply #5 - Jan 6th, 2018, 8:06am
 
The heat store provides the heat so can't be taken out of the equation!  Not a new system but an existing one. Just that he's changed things a bit!

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Re: Who's right ?
Reply #4 - Jan 5th, 2018, 9:10pm
 
One other thing you should try is holding a bottle of water under the vent pipe and get someone to turn the pumps on and off.

I only wish you had asked an opinion about sludge buckets, (thermal stores) I don't think you would have gone for it.

Insulation in unheated spaces is critical to any system.

If you getting air that can't be removed it hasn't been installed correctly.
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Re: Who's right ?
Reply #3 - Jan 5th, 2018, 9:03pm
 
Is there a lockshield valve on the store return because it looks as though that circuit would pinch the lions share of the flow.

Have/can you try the heating only without the store being on.

Trying to understand it is difficult and certainly, I would say a likely problem as he's restricted the heating flow ( I think)
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Re: Who's right ?
Reply #2 - Jan 5th, 2018, 4:43pm
 
My drawings are lousy!  Just think of the flow as coming from the heat store (Akvaterm) then up that vertical red arrow, down the pink arrow to the hw cylinder area. There it goes to the pump and after the pump the usual split CH/HW with two motorised Honeywell valves.  The fuzzy grey line is the CH feed after the Honeywell valve and it connects into the original CH system flow halfway down.

It's a tad academic now as he came round yesterday and he and his son spent a good 3-4 hours getting rid of the air in the system. Involving hosepipes and suction pumps. This air was partially blocking the return...once it was out of the way the whole system sprung to life with good heat in all radiators.  

We had the heat loss discussion. I came at it by describing a system where there was 500 yards of copper pipe between heat store and the first rad. Eventually he agreed with me. But we then had the further discussion about the discussions we'd had at the outset. There were the three options - as he reminded me.

Option A - keep the pump at the heat store and run two pipes down to it to create the neutral point. Trouble was that given all the steel etc in the building getting a clean run back - especially for the vent pipe that needed a gradual upward slope - was nigh on impossible.

Option B - the one we went for. Move the pump up to the area of the HW tank (where the feed and vent pipes were), make the tweaks to the circuit as outlined above. The option we went for. What I am a bit annoyed about is that he didn't point out to me the implications re heat loss in the changed circuit - especially as it was he who suggested the use of the heat store to run the boiler fully in condensing mode etc. This heat loss may mean that I can't run the boiler as efficiently as I wanted to and I've wasted all that money. Time will tell. He suggested that with the improved flow rate that it might not be as bad as it was. Fingers crossed.

Had I known about the heat loss then I guess I could have tried a bit harder to find a way to go the Option A route. Hard call. I do know that I tried damn hard the first time round (it was possible pump noise that was the driver as LOML has the hearing of a barn owl).

Option C - a pressurised system. Which, as previously mentioned, was ruled out due to unknown existing pipework provenance. We shall see...may have to bite the bullet and go for it downline.


That was yesterday and all tickety boo.  Then today I needed to turn the pump off.  When I turned it back on, the old symptoms came back so there is clearly still air in the return.  Bit bloody annoying as we had good heat from upstairs and downstairs rads but now downstairs are cold and upstairs tepid at best.  

Anyway, if you're still with us (!) back to that heat loss.  If I got a pump with a faster flow rate then the water wouldn't lose as much heat?  Yes?  No ?
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