megaflow direct hot water - I think

Hi, I've got a hot water cylinder without a hot water topper tank - it' s a "Tribune Premier" by IMI waterheating - about 10 years old. a mate of mine said this is sometimes called megaflow. Does the hot water that I use actually sit in that tank - all 160 litres of it - at mains pressure? Or does the water I use sit in a coil within the tank directly connected to the mains supply and heated by the hot water from the boiler in the tank as I use it? Put it this way, my two showers in my house are very forceful and it only takes a couple of minutes to fill the bath. It is definitely not a combination boiler, i.e. the boiler does not come on when I want hot water. IF the mains water is heated by the tank contents as I use it, why don't I get a blast of really hotly water when I first run the shower (water that would have been sitting in the coil in the tank)? The other day I had to change taps downstairs. I switched the water off at the mains stop c*ck and ran the hot water. Only about two buckets full's came out.

On megaflow, if I add central heating inhibiter, does that get mixed to the heating contents of the hot water system? Is the hot water system a different hot water circuit, not connected together to the central heating? IF that's the case how would I get to drain the hot water cylinder? When I drained the radiators the other day, there didn't seem to be an excessive amount of water as would be the case if the cylinder was being drained.

My house is a common or garden modern detached house, 10 years old.

Confused... !!!! Steve

Reply to
Keyser Sose
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There is a tapo at the bottom of the cyclinder. IS this the way to empty it?

Reply to
Keyser Sose

On Wed, 13 Dec 2006 10:07:26 -0000 someone who may be "Keyser Sose" wrote this:-

Yes. Assuming it is an "unvented" cylinder, which is probably the case.

Unlikely given the age of the installation.

Other water may be trapped in the pipework. Did you open an upstairs tap while draining down?

It will be mixed with the water in the coil in the cylinder. It will not be mixed with the water in the taps.

The water in the shell of the cylinder, or the coil?

Reply to
David Hansen

If it's an unvented HW system then two buckets might be all that is needed to work on your taps.

I had an unvented "primatic" type system whereby the central heating was topped up by the water in the HW tank. For those systems you can't add inhibitor because of the possibility of contamination. I doubt yours is like that but you might want to check. You should either have a small header tank or a separate pressure vessel for the CH and a pressure vessel or "bubble" for the HW.

Megaflow is a model name of Heatrae I think and the correct general term is unvented cylinder.

Reply to
adder1969

The way the mains pressure systems work is that there is

(i) a tank full of water fed directly from the mains which gets heated by

(ii) a completely independent loop of pipe that is connected to the boiler and CH system..

(iii) which will have motorised valves that control which circuit is open to the boiler and pump, usually with a tank thermostat to halt the flow when the tank is hot enough.

That will be pressurised to a little below mains pressure - there is usually a pressure gauge on the boiler.

When you add inhibitor, it's to this 'primary' circuit..this is a closed loop of water that heats the cylinder and the rads and never gets replenished unless you drain down the primary (as you envisage) to add inhibitor.

No..its a different circuit.

Yes and no..the PRIMARY coil is part of the CH, but separated from it by control valves.

The actual hot water is just a tankful of hot water at mains pressure.

There wouldn't be. You never drained the tank at all. In fact its quite hard to do and you wouldn't ever normally need to..

I did mange to do it however all over the bathroom floor when I turned off the incoming water to the house, and flushed a loo downstairs..my tank is in the loft and the hot water fell out as soon as the ballcock downstairs opened to let air INTO the tank.

The way to empty a tank is to open TWO taps at least one of which is below the level of the tank base, after turning OFF the mains water supply. The tap at the base is probably there in case that IS the lowest point - you can put a pressurised HW cylinder almost anywhere in a house..including the basement if you have one.

Relax. You have teh best water sysrem there is IMHO.

I would consider, if in a had water area, fitting a full flow softener to the incoming mains feed..those cylinders are expensive and scale will eventually get you.

Reply to
The Natural Philosopher

Thanks for the replies guys. Yes there is one small (bucket sized) header tank in the loft that gets emptied when I drain the radiators. Yes, there is an expansion vessel connected to the hot water cylinder. So when I have a bath I use the actual 160 litres of hot water that was contained in that cylinder? How on earth can that water be under mains pressure? And if the water in that cylinder is stored for my use, how come only two buckets came out when I closed off the main stop c*ck and ran the hot water downstairs?? Why didn't it drain the entire cylinder?

My mate reckons the water I use is actually heated as it flows through a coil inside the cylinder. The bulk of the contents of the cylinder are just to heat the water in the coil of pipe, that coil being under mains pressure and directly connected to the mains (the exact opposite of the old indirect system). The contents of the cylinder go down to be heated by the boiler but I do not have a bath in that water at all, it;so just used for heating the contents of the coil..... ?????

Complex stuff this plumbing. And very interesting too !!! :-)

Steve

Reply to
Keyser Sose

On Wed, 13 Dec 2006 12:08:14 -0000 someone who may be "Keyser Sose" top-posted this:-

Hopefully not all of it, but a fair proportion of it.

How can water in pipes be under mains pressure? Because they are strong enough to withstand the pressure.

Probably because you didn't open up anywhere to let air in. For the water to flow out either air has to be let in, or the pipes crushed flat.

What does your mate know about water heating systems?

He or she has described a thermal store. I doubt if you have one, but you may do.

Reply to
David Hansen

That is the header tank for the radiator ('primary') circuit. There is essentially a 'radiator' inside the cylinder, that heats the stored

160 litres of Domestic Hot Water. These 2 waters do not mix.

To allow for expansion of the Domestic Hot Water as it is heated. Since the system is un-vented, without an expansion vessel, the pressure could rise to dangerous levels as the water is heated. There will be an emergency pressure relief valve venting out via a tundish to protect against this eventuality.

Yes.

The cold feed to the cylinder comes directly off the mains supply ( usually via a 3 bar regulator to limit the normal working pressure. )

Because the hot draw-off is at the top of the cylinder. Without any pressure being applied at the inlet, the tank cannot drain up the way.

You will get some volume of water draining out, as a result of:

1) The pipe volume from the tank down to the tap ( you may get some more if you also open an upstairs hot tap, and allow air in. You will then get some further pipe volume draining out. 2) The expansion vessel relaxing to it's un-pressured state.

Such systems do exist, but I don't think that is what you have. And those are not 'megaflo' systems.

I think what you have is a megaflo-type system ( but from another manufacturer. ) A megaflo is one company's ( Heatrae Sadia ) brand name for it's range of unvented HW cylinders, which work the way we have described.

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The contents of the cylinder go down to be heated by the boiler but I do

I don't think this is what you have. I think you have a megaflo-equivlant unvented cylinder. ( The expansion vessel is 1 clue. Also, there will be expansion relief valves and Temp / Pressure relief valves with test knobs on them , draining into a cone-shaped plastic cup thing called a tundish. If these are present, then for sure you have an unvented indirect cylinder. )

If you were to post some photos on the web, we could see better. What does any labeling on the cylinder say?

Reply to
Ron Lowe

Ah. Interesting so the primary is not pressurised, but the DHW is?

Yes.

Its connected to the mains?

Vaccuum. Nothing to replace the water with,..if you had also opened a hot water tap upstairs...:-)

Could be, but I have never heard it done that way..

Reply to
The Natural Philosopher

He is describing a thermal store, which have been around for well over 10 years.

Reply to
Doctor Drivel

An unvented primatic? I think you mean no F&E tank needed.

Reply to
Doctor Drivel

Yes, that's part of it, but not the whole story.

Opening a downstairs tap will drain a certain volume untill the accumulator is exhausted, and then a certain percentage of the pipe volume untill it vaccuum-locks. Opening an upstairs tap at this point will let air in the top, and the remaining pipe volume will then flow out the downstairs tap.

At this point, the pipe-work is empty.

But the tank itself will remain full. There's nothing to push the water UP out the draw-off at the top.

The only way to drain the tank is to have a drain-c*ck fitted at the cold feed, which is at the bottom.

< use fixed font >

------------- | Expansion | T |~~~~~~~~~~~| =====X | | |Upstairs hot tap ------------- | | | | | |========================| | | | | ------|------- | | | | | | | | | | | | | =========== | | | / | | | \ | | | / | | | \ | | =========== | | | | | | | Valve Closed | | | | | |

Reply to
Ron Lowe

On Wed, 13 Dec 2006 14:18:38 -0000 someone who may be "Doctor Drivel" wrote this:-

Possibly.

As I went to the trouble of typing about two hours before you made that comment, "He or she has described a thermal store. I doubt if you have one, but you may do."

Reply to
David Hansen

He clearly was.

A Gledhill Systemate. with a Landis & Gyr outside weather compensator on the CH, heated by an Ideal Minimiser condensing boiler.

Reply to
Doctor Drivel

I agree, he was describing a Thermal Store, as proposed by his clueless 'mate', who also described the same configuration as a 'megaflo'. This ought to tell us something about the 'mate', and also something about the actual installation.

Why did you just list a bunch of random components? The OP mentioned none of the above.

He did, however, describe the cylinder as : "Tribune Premier" by IMI waterheating - about 10 years old.

How does that figure in your random list of components?

Do you really think that is what the OP has, based on the description? Where does the expansion vessel on the DHW he mentioned figure in this scheme?

In short, what was the purpose of that random list of components, since it clearly has no bearing on the OP's situation?

Reply to
Ron Lowe

I was asked a question and answered. Please read properly.

You are a very confused person, peoplel with names like Ron usually are.

Reply to
Doctor Drivel

Yes, in the same way that a vacuum cleaner is frequently called a hoover. It's an unvented HW cylinder bit not a genuine Heatrae Sadia Megaflow.

Does the hot water that I use

No. That's a heat bank or thermal store.

Put it this way, my two showers in my house are very

That's the HW expansion volume/vessel expanding to atmospheric pressure. All is well. Usually there is a valve installed on the HW outlet so that you don't waste so much water when you need to perform maintenance.

The heating system is almost certainly a sealed system. See FAQ! The only contact between the heating system and the "megaflow" is the indirect coil inside the cylinder, the waters do not meet.

Is the hot water system a

Part of the heating system heats the cylinder. The water in the cylinder comes from the mains and goes out the hot taps.

IF that's the case how would I get to drain the hot water

In the unlikely event that you need to do this there is probably a drain point at or near the bottom of the cylinder or supply pipe.

When I drained the radiators the other day, there didn't seem

See Sealed CH FAQ. What's wrong with the heating or do you just like taking things apart? If ain't broke don't fix it especially at this time of year.

A modern house properly plumbed to modern standards.

Reply to
Ed Sirett

Reply to
Ed Sirett

MAny thanks for the replies guys. Darined down becaise I installed three new radiators and was perplexed that so littlke water came out, also when I changed the taps was expecting to drain the hot water cylinder.

Yes do like taking things apart, but only if I am improvoing things. This new central heating system is a bit confusing !! Cheers, Steve

Reply to
Keyser Sose

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