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central heating heat loss

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Re: central heating heat loss

Postby RogerS » 12 Jan 2018, 11:35

Robert wrote:.....
So what controls are there? Manual at the momentIs 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 RogerS » 13 Jan 2018, 16:47

Here's an intriguing puzzle.

On another forum, one of the plumbing experts there asked me to dip the end of the vent pipe into some water and then turn the pump on and off and let him know what happened.

I'm not sure quite what I was expecting. Intuitively since the other end is at the neutral point I kind of expected nothing. What actually happened was that when the pump was switched off, bubbles came out and when it was switched on, the water was sucked up into the pipe.

And, of course, as I type this I can see what it happening but I'll let you puzzle it out for yourselves!
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Re: central heating heat loss

Postby Robert » 13 Jan 2018, 18:38

I did mention air getting sucked in previously i think. looking at where your fill pipe is though i was kind of discounting that.

The pump will compress any air in the system a little which will allow some new water intake. Turn the pump off and the air expands pushing air out of the vent pipe. maybe that means your rad system has a flow restriction as water comes from the vent easier than it gets round the rad circuit.

Probably coming from the vent as it has less resistance being a bigger pipe... or something is blocking the header tank outlet.
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Re: central heating heat loss

Postby RogerS » 13 Jan 2018, 20:02

I think that you are barking up the wrong tree, Robert.

We have a mass of water circulating through the system. When the pump stops, it effectively acts as a barrier to that flow of water which has inertia. This inertia carries some of it up into the vent pipe expelling a small amount of air from the 'downward' bit of the vent pipe (the bit hanging over the header tank).

When the pump resumes, again inertia plays its part as we have stationery water in the pipes. So there is momentarily an area of low pressure behind the pump..ie where the feed and vent pipes are connected. This has the effect of drawing that small amount water up into the vent pipe. Then the rest of the water starts moving and that point ceases to have a low pressure and becomes 'neutral'.
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Re: central heating heat loss

Postby TrimTheKing » 13 Jan 2018, 23:23

I don't have the brain capacity, please explain in words I can understand...
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Re: central heating heat loss

Postby Robert » 13 Jan 2018, 23:41

If you had a mass of water circulating then surely you wouldn't have under heating problems?

If the system is full of just water then water out of the pump has to circulate. Does it expand the radiators in that start up scenario?

The pump still allows flow when not running (I think) so I'm not convinced.

Ignoring arguments as to the cause...any improvement in the general heat output so far?
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Re: central heating heat loss

Postby RogerS » 14 Jan 2018, 07:08

Robert wrote:.....
Ignoring arguments as to the cause...any improvement in the general heat output so far?


Oh my goodness, yes. I had another go at bleeding the main pipes with the hosepipe and they're all working fine. Too much, in fact and have now turned most of them down and some off!

Working up the courage to simulate the room thermostat and switch off the pump for a while !
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Re: central heating heat loss

Postby Andyp » 15 Jan 2018, 08:25

JIT time Roger,

Looks like it could get a bit chilly up there this week.
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Re: central heating heat loss

Postby Deejay » 15 Jan 2018, 10:00

Morning Roger

There are no old valves or fittings left in the reused mains.

The vent and feed connections are OK.

What was once impossible to bleed is now bled. Sounds to me like the beggaring about with it has shifted a blockage. Mains water from your hose would bypass an airlock. but not easily go through a lump of sludge.

Get it hot on the highest pump setting and drain a bit off the rad's to see if the water is clean.

Fit a Magnaclean if you don't already have one.

Bleed it every few days until the air has gone.

Leave it alone. :D

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Re: central heating heat loss

Postby RogerS » 15 Jan 2018, 10:48

Deejay wrote:Morning Roger

There are no old valves or fittings left in the reused mains. No valves but couplers etc

The vent and feed connections are OK. Yup although on one forum he's insisting that the feed is blocked...which it isn't

What was once impossible to bleed is now bled. Sounds to me like the beggaring about with it has shifted a blockage. Mains water from your hose would bypass an airlock. but not easily go through a lump of sludge. I never fed mains (well, my pump pressure as it's my own water supply!) int the rad bleed valve. No sludge.

Get it hot on the highest pump setting and drain a bit off the rad's to see if the water is clean. Squeaky

Fit a Magnaclean if you don't already have one. Already fitted, thanks. Great believer in them

Bleed it every few days until the air has gone. Getting to the point where I am tempted to simulate the pump under room thermo stat control

Leave it alone. :D Good idea !

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Re: central heating heat loss

Postby Halo Jones » 16 Jan 2018, 15:22

Glad to hear all is working again. I really feel for you. We are renovating our house bit by bit and replacing the radiators as we go. Every time I drain the system I know that one of two radiators will get airlocked. It was on replacing my third radiator that I discovered if I get the rest of the system heating normally I can then turn them all off bar the one that was air-locked and that, along with a few bangs of the offending rad gave the pump enough oomph to clear the airlock. I've got another one to do next month and not looking forward to it!
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Re: central heating heat loss

Postby RogerS » 20 Jan 2018, 19:07

Plumber rang this morning to see how things were going as he had a day available on Monday. So we agreed that I'd turn off the pump to see what would happen.

An airlock.
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Re: central heating heat loss

Postby RogerS » 21 Jan 2018, 13:03

Just thought I'd give an update and a drawing of the system.

ImageHouse 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: central heating heat loss

Postby 9fingers » 21 Jan 2018, 13:22

A couple of points.
Unless the design of pumps has changed with these new fangled "a" rated expensive pumps, there is minimal constraint to flow when the pump is off.

An upstairs pump within a few feet vertically of the header tank is surely asking for trouble and get it pumping over or sucking in air.

I've always had downstairs pumps near the heat source and until now never come across this "neutral point" term/requirement.

Further thought..... if switching off the pump induces an airlock, then the running pump ressure must be trapping some air somewhere due to its running pressure, that when switched off get introduced to an "important " bit of the circuit and stop it functioning?

Second further thought. Is it the act of the pump starting up that is sucking in a fresh supply of air and causing the air lock that way? As a test, get the system working well, TEMPORARILY close off the vent pipe.
Now does stopping and restarting the pump induce an airlock?

Have you tried turning the pump down to minimum setting? Still got the problem?

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Re: central heating heat loss

Postby RogerS » 21 Jan 2018, 15:41

9fingers wrote:A couple of points.
Unless the design of pumps has changed with these new fangled "a" rated expensive pumps, there is minimal constraint to flow when the pump is off.

An upstairs pump within a few feet vertically of the header tank is surely asking for trouble and get it pumping over or sucking in air.It is an interesting idea and I immediately thought about all the points that you mention below...great minds and all that. I still will try it. BUT...a big but. At the suggestion of another guy over on another forum I stuck the end of the vent pipe into a small paint kettle with water in it...less than a litre which is much less than the volume of water inside the vent pipe. As I reported in an earlier post, when the pump was switched off, air bubbled out..when the pump was switched back on then the water (but not all of it) was drawn up into the vent pipe. Still...worth double-checking.

I've always had downstairs pumps near the heat source and until now never come across this "neutral point" term/requirement.

Further thought..... if switching off the pump induces an airlock, then the running pump ressure must be trapping some air somewhere due to its running pressure, that when switched off get introduced to an "important " bit of the circuit and stop it functioning? That's kind of what I'm thinking

Second further thought. Is it the act of the pump starting up that is sucking in a fresh supply of air and causing the air lock that way? As a test, get the system working well, TEMPORARILY close off the vent pipe.
Now does stopping and restarting the pump induce an airlock?

Have you tried turning the pump down to minimum setting? It's on minimumStill got the problem?

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Re: central heating heat loss

Postby Robert » 22 Jan 2018, 23:49

Just a passing thought....

If I understand it right you put a hose on the drain cock you have on the top of the towel rad and open it wide to allow a rapid drain to drag air out of the pipes..

Have you tried blocking the vent pipe during this process? Your vent pipe is wider than the fill pipe so maybe you are pulling air in when trying to get air out..
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Re: central heating heat loss

Postby RogerS » 23 Jan 2018, 08:05

The flow is not that rapid, Robert.

Just to recap. The plumber came round yesterday and spent a lot of the time scratching his head. To be fair to him, I'm in contact with a very helpful guy over on UKW who is a bit of a heating engineer expert. Even he is baffled.

We have two problems as I see it when it is in fault mode.

Problem 1...trying to 'fast' bleed by opening the return on the bleed rad, we get a few bubbles and then it stops. Nothing flows out. It can't be a blockage as far as we can see because when the system is running properly, every radiator is hot. It can't be a blocked feed pipe because we've checked that and it flows OK. There just does not seem enough head to push anything out. The plumber says that it's resistance in the pipes but I'm struggling to understand that because all we are looking at is a length of 22mm straight pipe and a reducing T to feed the 15mm radiator tail But flow there is not.

Problem 2 .... there is a block (airlock as far as we can make out) in the return of the CH pipes (having said that we need to check that the HW cylinder return is OK...we've not done that and that would help identify where, if any, the pipe is rising up then falling to trap the air). It takes luck to bleed that rad enough to free up the airlock.

He's going to try a more powerful pump. If that doesn't work then we need to regroup and start from first principles.

I've tried blocking the vent pipe when the pump starts in case any air was being drawn in....but it isn't.

Plan B is to temporarily cap the vent pipe and red pipe then pressurise the system and see if the pressure is maintained. If it is then will convert to a pressurised system.
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Re: central heating heat loss

Postby Robert » 23 Jan 2018, 09:53

RogerS wrote:The flow is not that rapid, Robert.

Problem 1...trying to 'fast' bleed by opening the return on the bleed rad, we get a few bubbles and then it stops. Nothing flows out.


I don't trust those drain cocks. They have a lump of rubber in them and it sticks/moves about. I removed ours and replaced them with full bore isolators. I can drain at full speed instead of a dribble. just push the hose on to a 15mm pipe stub.

Maybe turn off the rad valves and temporarily try some other drain tap?
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Re: central heating heat loss

Postby RogerS » 23 Jan 2018, 14:27

That's a very good point, Robert, re the washer.
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Re: central heating heat loss

Postby Deejay » 23 Jan 2018, 16:30

Afternoon Roger

Something simple to try. I can't find a smilie of somebody clutching at straws.

Regarding Robert's point about the MT cock, how is it oriented?

Normally they would hang below the thing they were supposed to drain, with the 'cylinder' and the screw you use to release it, in the vertical plane. The hose connection points down. The rubber seal sits below the valve seat inside the cock. When you open the valve and flow starts, the water tends to keep the valve open. The better quality cocks have a rubber washer on a disk which is loosely fitted to the shaft of the valve, so it will move up an down the shaft for one or two mm.

You say that opening the MT cock allows a few bubbles and some water out and then stops.

Its hard to tell from the picture, but could the MT cock be upside down? What if the static head, of probably about six feet, isn't enough to overcome gravity and the valve closes? If this is happening it would also explain why sucking on the hose connection allows the flow to start again.

Open it till the bubbles/dribbling stops. Open it a bit more and tap it to see if it starts again.

If that doesn't work, close it (DAMHIKT) , turn on the pump and try again.

If that doesn't work, you've wasted ten minutes but it's one less thing to worry about.

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Re: central heating heat loss

Postby RogerS » 23 Jan 2018, 20:13

Here's the drain cock arrangement, Dave

Image
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Re: central heating heat loss

Postby Deejay » 24 Jan 2018, 09:39

Roger

Are the 'fins' horizontal or vertical?

If they are vertical, is the MT cock at the top of the rad?

A picture of the entire rad showing the floor would be useful.

Have you tried my suggestion?

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Re: central heating heat loss

Postby RogerS » 24 Jan 2018, 09:42

Deejay wrote:Roger

Are the 'fins' horizontal or vertical? horizontal

If they are vertical, is the MT cock at the top of the rad? N/A

A picture of the entire rad showing the floor would be useful.

Have you tried my suggestion? Not yet. Will wait until plumber is back as it's all working at the moment!

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Re: central heating heat loss

Postby Deejay » 24 Jan 2018, 09:57

Roger

If the body of the cock is horizontal, gravity won't move the washer to reseal it.

It was a long shot anyway.

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Re: central heating heat loss

Postby RogerS » 24 Jan 2018, 10:12

Deejay wrote:Roger

If the body of the cock is horizontal, gravity won't move the washer to reseal it.

It was a long shot anyway.

Cheers

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I still think there might be some mileage in your suggestion as in my experience some of these drain cock have the washer/plunger part floating wrt the dooberry that you turn to undo the drain cock. So possibly sticking ?
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