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central heating heat loss

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Re: central heating heat loss

Postby Deejay » 07 Jan 2018, 10:50

Morning Roger

I'd forgotten that you were using the heat store. I assume that it's a fully pumped system.

It does seem to be an airlock problem doesn't it. Do you know if the system ever worked properly? The worst case scenario seems to be poor installation of the heating mains. Before you take up the floors to check, do all the basic things. I know you have done them before, but you have to start somewhere. There is now a lot of live water in the system, full of air, which will take time to come out.

Bleed everything again. Keep bleeding every day to see if you can eliminate the air. You'll soon find out if most of the air collects in a particular radiator, which would help with locating airlocks.

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Re: central heating heat loss

Postby RogerS » 08 Jan 2018, 18:29

Deejay wrote:Morning Roger

I'd forgotten that you were using the heat store. I assume that it's a fully pumped system.

It does seem to be an airlock problem doesn't it. Do you know if the system ever worked properly?


Yes it did.

Deejay wrote:The worst case scenario seems to be poor installation of the heating mains.


It has to be something to do with the change in the way the main feed is connected to the rad circuit.

Deejay wrote:Before you take up the floors to check,


That's not going to happen ! I still have access to some areas but the critical area where they cut one of the pipes is now behind plaster.

Deejay wrote:..... There is now a lot of live water in the system, full of air, which will take time to come out.

Bleed everything again. Keep bleeding every day to see if you can eliminate the air. You'll soon find out if most of the air collects in a particular radiator, which would help with locating airlocks.

Cheers

Dave


It's not in any radiator but something to do with the main rad circuit. I made the mistake today of going round fitting TRVs to some of the rads as they were blasting out heat. This included the heated towel rail in the en-suite and this is the one that I do the hosepipe bleed on. Well guess what....fitting the TRV had the same effect as switching off the pump as I've just discovered that the rads are failing again.

So tomorrow morning it's start bleeding the system all over again. Bugger.
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Re: central heating heat loss

Postby RogerS » 08 Jan 2018, 19:54

Had a go this evening. Failed miserably. Given up. Who needs central heating anyway ?

Sodding plumber. At least I still have £1250 still to pay him.
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Re: central heating heat loss

Postby Robert » 09 Jan 2018, 00:00

So is this still a case of very low flow?

I know air is the main suspect but just wondering if there is a blockage somewhere?

You are re-using the existing heat store but is there lots of old pipe too or all new? I used to have a simple mesh filter in the return pipe to the boiler (fitted by the boiler installer) and it took no time at all to become blocked and need cleaning. I'm guessing you must have a proper magnetic filter (as I now have) but is it still clean?

Which reminds me it is probably time I cleaned mine again.

Are all your rads the same make? Any chance they are restricting flow?

Could there be some lump of crud in the pipe and you move it when you 'power bleed' then it drifts back to block somewhere?
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Re: central heating heat loss

Postby RogerS » 09 Jan 2018, 07:21

Robert wrote:So is this still a case of very low flow?

I know air is the main suspect but just wondering if there is a blockage somewhere?

You are re-using the existing heat store but is there lots of old pipe too or all new? I used to have a simple mesh filter in the return pipe to the boiler (fitted by the boiler installer) and it took no time at all to become blocked and need cleaning. I'm guessing you must have a proper magnetic filter (as I now have) but is it still clean?

Which reminds me it is probably time I cleaned mine again.

Are all your rads the same make? Any chance they are restricting flow?

Could there be some lump of crud in the pipe and you move it when you 'power bleed' then it drifts back to block somewhere?


Many thanks for all the suggestions, Robert, but it a repeating airlock in the main feeder pipe on the return.
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Re: central heating heat loss

Postby Deejay » 09 Jan 2018, 10:25

Morning Roger

So you don't get any air out of the radiators ?

Your plumber re-positioned the feed and vent pipes. I assume they now connect somewhere on the upstairs mains. IIRC conventional wisdom in the seventies was to connect the feed pipe low down on the system so that the water would expel all the air up through the vent as it filled. If your feed is connected upstairs it will be trying to fill the downstairs rad's from above. Slowing down the fill rate might help.

Have you tried backfilling from an MT cock on a downstairs rad?

PS If you suspect sludge causing a blockage, see if a magnet will stick to it, where you can get at the pipework.

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Re: central heating heat loss

Postby RogerS » 09 Jan 2018, 11:30

Hi Dave

No....tiny amounts that you'd expect from time to time as the system settles down. No, to get rid of the air in the main feed pipe you have to remove the 'block' that the normal bleed valve presents to the system. This is now a standard fitting in all good homes

Image

Yes, upstairs. Here's the arrangement for the neutral point.

Image

No sludge in the system. Besides if there was I'd really be in deep doodoos as the main pipes are 28mm and 22mm.
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Re: central heating heat loss

Postby 9fingers » 09 Jan 2018, 12:52

Not sure I understand why a bleed valve presents a block in the system?

Now that you know where the air is accumulating, you can fit a bleed point there, with or without a dead leg according to whether you feel that air might collect there over time or not.

It is bad enough to have a system that can airlock whenever you do anything to it but one that can gradually build up an air lock surely needs attention for peace of mind.

I'd not come across the term "neutral point" before but have read up on it now. Both my vented systems have had the pump on the return and located near the heat source with The F&E and overflow pipe joined in up stairs in a convenient location usually on the gravity feed DHW loop.

I recently changed to both a pressurised system and pumped DHW when I put the new boiler in a few years back and the solar thermal store was added.

None of my systems seemed to have experienced the degree of grief that you are experiencing - maybe more by luck than design?

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Re: central heating heat loss

Postby RogerS » 09 Jan 2018, 13:31

9fingers wrote:Not sure I understand why a bleed valve presents a block in the system?

.....
Bob


The tiny outlet in the bleed valve gives a high-impedance (for want of a better term) and if there is not enough head in the system then it wont flow out that easily. Want you need here is a good whoosh to get it all flowing nicely and to carry the air out.

It is that bad that even with the hosepipe connected there is sometimes no flow even then. You have to fit a suction device on the end of the hose to draw the water/air out.
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Re: central heating heat loss

Postby 9fingers » 09 Jan 2018, 13:44

RogerS wrote:
The tiny outlet in the bleed valve gives a high-impedance (for want of a better term) and if there is not enough head in the system then it wont flow out that easily. Want you need here is a good whoosh to get it all flowing nicely and to carry the air out.

It is that bad that even with the hosepipe connected there is sometimes no flow even then. You have to fit a suction device on the end of the hose to draw the water/air out.


Difficult to credit that either present a problem.
How many feet of head do you have from header tank water level to the point where bleed point wont work?

Maybe a pair of valves on the output of the header tank to switch from open vent to pressure regulated mains water solely when filling?

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Re: central heating heat loss

Postby Robert » 09 Jan 2018, 16:20

I'd never heard of Neutral point either and without extensive reading I'm still not sure what it is.

I don't really get the air lock thing either in a radiator circuit. When I empty and refill our system (open vented conventional boiler rads and cylinder) there is usually air in the pipes afterwards. The pump runs and the pipes gurgle - sometimes for a couple of days. The air ends up in rads and I bleed it out. job done. What I don't get with yours is, if the pump is pushing out water - it has to go somewhere. It should push the air along in the pipe with it. the air may bubble back up the pipe but it can't block it. If the pump ends up pumping air then yes there will be no flow. As I said if there is water at the pump it must be going somewhere. How can air stop it?

Also, you have had it working so how does air get back in? could the pump be drawing water down a vent pipe enough to suck in air? Tried temporarily capping the vent pipe? Any overflow from the expansion tank to indicate water being replaced by air?

Before I moved the expansion tank there was about 3ft of head to the top of the tall towel rad in the bathroom and that was plenty to bleed it so I can't see why you need fast venting either.

Any chance of a line drawing of the whole system? not to scale, just showing what connects to what.
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Re: central heating heat loss

Postby Deejay » 11 Jan 2018, 13:16

Morning Roger

Am I right in assuming that the direction of the flow is down to the heating circuits?

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Re: central heating heat loss

Postby RogerS » 11 Jan 2018, 13:50

Robert has asked some very cogent questions and some I can'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 ?

Image

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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Re: central heating heat loss

Postby RogerS » 11 Jan 2018, 13:51

Deejay wrote:Morning Roger

Am I right in assuming that the direction of the flow is down to the heating circuits?

Cheers

Dave



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Re: central heating heat loss

Postby Robert » 11 Jan 2018, 15:27

You've confused me with your drawing :)

The photo above labelled neutral point shows a pump with vertical pipes and doesn't look like the pump could be left sitting in air.

Your drawing however shows a pump that is bound to sit in any air in the pipe and therefore pump nothing.

Do you have 2 pumps?

And even with your additional reading I still can't see how air can stop heating flow if the pump is powerful enough to overcome any head - which I'm sure it would be.
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Re: central heating heat loss

Postby RogerS » 11 Jan 2018, 16:03

Robert wrote:You've confused me with your drawing :)

The photo above labelled neutral point shows a pump with vertical pipes and doesn't look like the pump could be left sitting in air.

Your drawing however shows a pump that is bound to sit in any air in the pipe and therefore pump nothing.

Do you have 2 pumps?

And even with your additional reading I still can't see how air can stop heating flow if the pump is powerful enough to overcome any head - which I'm sure it would be.



No just the one pump. I have exaggerated the slope. I'm afraid that air locks happen. Examples of people asking how to fix them are all over Google.
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Re: central heating heat loss

Postby Deejay » 11 Jan 2018, 17:06

RogerS wrote:
Deejay wrote:Morning Roger

Am I right in assuming that the direction of the flow is down to the heating circuits?

Cheers

Dave



Don't follow you, Dave


Does the arrow on the pump point downwards?
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Re: central heating heat loss

Postby RogerS » 11 Jan 2018, 17:12

Deejay wrote:
RogerS wrote:
Deejay wrote:Morning Roger

Am I right in assuming that the direction of the flow is down to the heating circuits?

Cheers

Dave



Don't follow you, Dave


Does the arrow on the pump point downwards?


Yes it does.
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Re: central heating heat loss

Postby Deejay » 11 Jan 2018, 17:27

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

Image

Any air collecting in or above the pump would be vented away, according to the photo.

On the sketch you show a pipe from the top of the pump down to an elbow and then up to a tee. Where does the pipe from that tee labelled 'uphill again' go?

Rollercoasting is a good description. In an ideal world, the heating mains would have a continuous rise on the flow and a continuous fall on the return. In practice, if the flow rises to a radiator 1 and then falls to the next radiator 2, the flow pipe between the rad's will vent itself into rad 1 when the pump stops.

If the pipe between rad's falls and then rises, it (the pipe between rad's) will vent into one or both rad's.

Real problems arise if the main pipes rise and then fall again between rad's or between points at which the air can escape.

Cheers

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Last edited by Deejay on 11 Jan 2018, 17:36, edited 1 time in total.
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Re: central heating heat loss

Postby Robert » 11 Jan 2018, 17:35

If the flow is downwards...Your sketch shows flow to the pump input but there are 2 pipes (3 including what I guess is the fill pipe) going to the input in the photo. What are those pipes?

If it was pumped return it makes more sense as the heating and cylinder returns would come together.

The pump is the right way round?
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Re: central heating heat loss

Postby Deejay » 11 Jan 2018, 18:14

Afternoon Robert

As I remember it, the convention was to 'pump away' from the f/e pipe so it would appear to be right.

Looking at the picture water flows down the pipe below the pump . I assume that the 15 mm pipe runs up to the f/e tank and the 22 mm pipe runs up to the vent. The 22 mm pipe running down from the equal tee would therefore be the return from the rad's , as you say.

If you turn the pump round you'd probably get pumping over.

Roger

Are you sure that the pump is on the flow from the heat store?

Cheers

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Re: central heating heat loss

Postby RogerS » 11 Jan 2018, 19:27

Robert wrote:If the flow is downwards...Your sketch shows flow to the pump input but there are 2 pipes (3 including what I guess is the fill pipe) going to the input in the photo. What are those pipes?

If it was pumped return it makes more sense as the heating and cylinder returns would come together.

The pump is the right way round?


Does this help ?

IMG_20180109_101953.jpg
(91.77 KiB)


Pump is the right way round.

I wish I could remember how the hw and rads came together to become the one return pipe into the heat store.
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Re: central heating heat loss

Postby Robert » 12 Jan 2018, 10:11

Fair enough.

I ran the fill pipe down then up again to the connection to stop convection heating the header tank and my vent runs from near the boiler so I wasn't expecting your layout.

So what controls are there? Is there something to stop the cylinder taking all the flow and leaving none for the rads?
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Re: central heating heat loss

Postby Deejay » 12 Jan 2018, 11:18

Morning all

Roger

I think you mentioned that the DHW cylinder originally had separate flow and return pipes. (I can't find it in this post, hence the edit)

Was the HW circuit pumped or gravity fed? I've never fitted a gravity fed HWC but I think they had a non return valve in the circuit to stop heat escaping back down to the boiler. I think they also used a thermostat in the return (?) pipe to stop the flow when up to temperature.

Since you are reusing the old DHW piping, could there be anything left in the pipe work?

Is there a non-return valve fitted in the new circuit from the heat store?

Is that a new self regulating pump? If so, can you override it and set the speed to continuous until you sort out the airlock?

Cheers

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Re: central heating heat loss

Postby RogerS » 12 Jan 2018, 11:34

Deejay wrote:Morning all

Roger

I think you mentioned that the DHW cylinder originally had separate flow and return pipes. (I can't find it in this post, hence the edit) Yes they did

Was the HW circuit pumped or gravity fed? pumped I've never fitted a gravity fed HWC but I think they had a non return valve in the circuit to stop heat escaping back down to the boiler. I think they also used a thermostat in the return (?) pipe to stop the flow when up to temperature.

Since you are reusing the old DHW piping, could there be anything left in the pipe work? No flushed out

Is there a non-return valve fitted in the new circuit from the heat store?No

Is that a new self regulating pump? Ni idea. Grundfos USP2 15/60If so, can you override it and set the speed to continuous until you sort out the airlock? I just have three speed settings

Cheers

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