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Who's right ? (Read 1309 times)
londonman
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Re: Who's right ?
Reply #46 - Feb 9th, 2018, 9:58pm
 
It's quite straightforward if you remember that this is NOT a new system.  So there are stubs where some rads used to be and these will contain small amounts of air.

So you fill the system up from the header tank. Filling up ceases. Start the pump.  It will compress that air.  The header tank will deliver a bit more water into the system.  Now the system has more water in it than it should have in a 'steady state'.

Now the pump is turned off by the thermostat. Nothing to compress that air anymore and so that extra volume pushes the water back up the vent pipe and into the header tank.  Trouble is that the header tank is very small and not a lot of headroom between normal level and overflow.  So it overflows.  Then the cycle repeats drawing yet more air into the system.

One..to get rid of wherever the air is stuck will require taking off plasterboard.  All over.  I ain't going to do that.  Simples.  We're going to convert the system to a sealed system.
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Re: Who's right ?
Reply #45 - Feb 8th, 2018, 12:10pm
 
Nothing is sorted and won't be until the plumber goes back to base and gets the pipework re-installed as was.

Water cannot compress so if it's sucking water from the tank, where is it going? the same question in reverse, the tank is overflowing where is the water coming from.

The bigger pump was a bad idea, the pump is designed to the system duty, if it doesn't work then there's a problem with the system.

The plumber needs to look at the fault and work out what he's messed up.
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londonman
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Re: Who's right ?
Reply #44 - Feb 2nd, 2018, 1:31pm
 
The saga continues.

The good news is that the airlock problem has been sorted.  The pump starts up and gets heat to all the rads every time.  The only 'funny' as it were is that it makes a lot of noise when it first starts pumping.  Almost as if its cavitation or air but then once the water is moving it goes quiet.  Annoying, all the same.

The bad news is that we're getting pumping over.  I came across this by chance as I popped outside and saw that the header tank was overflowing.  When I went into the loft, the water was high and warm.  The pump at this time was off.

So I fired up the pump to see what would happen.  Lot of suction up the vent pipe, the water level in the header tank then dropped a lot ...enough for the ballcock to drop and let in fresh water.

I let the pump run for a while to ensure everything was at operating temperature and then switched the pump off.  Hot water then rushed out of the vent pipe and filled up the header tank...enough for the overflow to kick in.  The cycle then repeats.  Obviously we are constantly introducing new water into the system which is not good, as you know.

My laymans' guess is that when the pump stops it acts as a brake to the circulating water flow and momentum in that circulating water then rushes up the vent pipe.  This happens because the pump is upstairs and so there is not that much head in the vent pipe to stop this happening.  If the pump was downstairs then the weight of water in the vent pipe would act as a damper and pumping over wouldn't happen.  Is this a reasonable deduction?

So...solution ?  I can't see how a bigger tank will help as we'll constantly be introducing air into the circuit by virtue of the water cascading out of the vent pipe in the open air.  Sealed system?
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londonman
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Re: Who's right ?
Reply #43 - Jan 29th, 2018, 2:51pm
 
It isn't...well, tiniest amount when the pump starts up but what one would expect and certainly only a few cc and not enough to clear the pipe out of water.
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Re: Who's right ?
Reply #42 - Jan 28th, 2018, 10:01pm
 
Did he check the vent wasn't drinking the water from the jar.
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londonman
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Re: Who's right ?
Reply #41 - Jan 28th, 2018, 11:54am
 
Sorted !

Plumber fitted a more powerful pump yesterday albeit much more expensive.  Reasoning went that (a) we knew there was air in the system - from dissolved air in the fresh water being introduced when we hose-pipe bled but (b) the initial pump wasn't man enough to push the air out from wherever it had accumulated.

So...more powerful Grundfos pump and bingo...ran the pump at its highest speed and system worked just fine.  Let it get back up to temperature and then switched it off for 30 minutes.  Turned it back on and rads warmed up everywhere...upstairs and downstairs. This morning I turned it down to its lower speed and repeated the test.  Again..all rads returned to normal working.  No hose-pipe bleeding required !

There are also several unexpected bonuses.

1) Any air in the system either goes up the vent pipe or accumulates in the top of that radiator I was using to hose-bleed.  A doddle to bleed the air out now.

2) Because it's running the water through faster, means that there is less time for that central main pipe to lose heat in an unwanted area.  The rads seem hotter as a result.

3) Saturday morning woke to find the trip in the garage gone.  Further inspection revealed that the old circulating pump we'd pressed into service for the boiler primary circuit had burnt out.  The pump we took out from indoors has now replaced it !  Just got to take the new one I'd bought Saturday morning back to see if I can get a refund.  Plumber called me while I was on my way back...too late to avoid the purchase.
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londonman
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Re: Who's right ?
Reply #40 - Jan 22nd, 2018, 1:53pm
 
It's an Akvaterm...2500 litre.  But all that is connected is a coil inside it that comes out to the flow and return pipes for the HW cylinder an CH.   You are correct in that the Akvaterm and boiler are on a separate circuit with their own open vented system.  

We tried feeding the flow into the other CH pipe - just in case the original pipe tapped into wasn't the flow.  If anything it made things worse.

He's talking about a more powerful pump to push out any airlock as we are in Catch-22.  If we beed the radiator to remove the airlock then that introduces fresh water into the system which will release any dissolved air which will form another airlock which will .....

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Re: Who's right ?
Reply #39 - Jan 22nd, 2018, 11:01am
 
The longer this goes on the more I think he messed up somewhere.

What is the make, model and size of the store please.
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Re: Who's right ?
Reply #38 - Jan 22nd, 2018, 10:55am
 
Valves on the magnaclean are fine.

To be perfectly honest I don't know why you have a vent or neutral zone. The store heating circuit doesn't need it, and I can't see any connection for the boiler to store, which must have a vent or other safety devices elsewhere.

Can you tell me is it a two or one pipe system. You would need to check one of the old rads to tell whether it has 2 pipes serving it or if both tails are connected to the same pipe.
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Re: Who's right ?
Reply #37 - Jan 22nd, 2018, 9:22am
 
thescruff wrote on Jan 22nd, 2018, 12:39am:
Unfortunately, I don't have enough information to answer your question, you could feel the radiator tails to see which end gets hot first.  Tricky as I did not take any notes as to flow/return on the rads when the original system was running and no guarantee that the original installer got it right in the first place.  So I ensured that all the new rads and TRVs were bi-directional.  It was your comment re backflow or short circuit that made me wonder about possible mixing up between Flow and Return

What size pipe is the flow from the store and can I assume there are no valves of any description on it.  22mm . Yes, on the Magnaclean

The first problem is to get the plumber to sort the sucking air in. For what it's worth it should be labour free.  I agree.  For what it is worth, I temporarily capped the end of the vent pipe (to eliminate air being sucked in from there at pump switch on but no cigar



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Re: Who's right ?
Reply #36 - Jan 22nd, 2018, 12:39am
 
Unfortunately, I don't have enough information to answer your question, you could feel the radiator tails to see which end gets hot first.

What size pipe is the flow from the store and can I assume there are no valves of any description on it.

The first problem is to get the plumber to sort the sucking air in. For what it's worth it should be labour free.


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Re: Who's right ?
Reply #35 - Jan 21st, 2018, 9:59pm
 
The blue pipe is marked Heat store return.  It is the combined return of the CH and cylinder.  The HW cylinder return is shown in blue ..it's the pipe that ends below the D in Downstairs.  

When I bleed the 'bleed rad' I will turn off the TRV and the lockshield.  

1) Then just open the lockshield.  See if I can get that flowing again (usually needs suction).  

2) Then turn of the lockshield.  Turn the TRV on and try to get some flow out of that.  

3) Repeat 1 until it all starts working again.

The backflow is VERY interesting.  The modification to the CH flow now introduces it halfway down ...see this and earlier diagrams.  Now what if he cocked up and that it isn't the original flow that he has tapped into but, in fact, the return ?
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Re: Who's right ?
Reply #34 - Jan 21st, 2018, 6:31pm
 
I'll try and get my head around the drawing.

A, it all looks wrong, so I'll do some imaginary connecting.

What is the blue pipe from the store running alongside the flow, and where how does it connect.

Where does the HW return connect, I assume by HW you mean the cylinder.

The pump should always be off when bleeding.

If there's an airlock say in the flow or return pipe leading to the bleed rad then water will still come out the other pipe so you need to shut one valve to draw the air out. so, if the return is airlocked you need to turn the flow valve off, or vice versa.

Your plumber needs to sort why it's pulling air into the system.

Guessing at this time but it looks like you may have cross connections that are causing a backflow or short circuit
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londonman
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Re: Who's right ?
Reply #33 - Jan 21st, 2018, 12:04pm
 
Just thought I'd give an update and a drawing of the system.

...House ch layout

Where it says 'other rads' these are upstairs ones.  Flow from heatstore is hidden by the heatstore return pipe.

The radiator marked 'bleed' rad is approximately in the right position and is the one (a) highest in the circuit and (b) furthest rad upstairs from the pump.  My plumber called me up yesterday to see how things were going as he has a free day tomorrow. We agreed that I'd try switching off the pump to see what happened.  Answer....an airlock when I started it up again.

I have a permanently connected drain cock in place of the bleed valve on the 'bleed' rad.  So connect up a hose and open the lockshield.  Some air bubbles and then nothing.  No more air.  No water.  Remember the system has been working fine and that radiator was hot and so has water in it.  So there's not enough head to push out any water/air in the pipes..  Unless ....unless  :idea:   you switch the pump off when you bleed, yes ?  In that case doesn't the pump act as a block to the flow...which explains why nothing comes out ?  But then surely the head in the tank is still acting to push the water out as it's acting back through the flow from the heat store, through the heat store and back up the return to that bleed rad...so it should vent.  You have to stick suction on the end of the hose to get it flowing again,whereupon air and water comes out of the hose/lockshield route.

This time was also different in that when I closed the lockshield and opened the flow on the rad, I got a lot of air out.  Very confusing
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Re: Who's right ?
Reply #32 - Jan 14th, 2018, 8:57am
 
No that is the normal combination, bigger systems could be 22/28.
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londonman
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Re: Who's right ?
Reply #31 - Jan 14th, 2018, 2:32am
 
Does it make any difference if the cold feed is 15mm and the vent 22mm ?
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Re: Who's right ?
Reply #30 - Jan 13th, 2018, 11:09pm
 
Image 5   

Assuming the flow/pump is the direction marked, then the problem as said is likely in the circle, eg blocked/restricted cold feed.
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