Can someone explain how my HW and CH system works, please?

[miljee]

Numpty alert!

I am from 'sunnier climes' where we don't have CH, & I have recently moved into a UK house where I don't get how the CH&HW system 'works' (though it does!).

We have, in the garage, a Potterton 'boiler' (thing with the pilot light). In the loft is a pressurised Megaflo. The 14 radiators are, apparently pressurised as well (the house is about 12 years old and the Megaflo is about 2 years old).

The Megaflo, we are told 'will heat up from cold in 30 minutes'. It has an electric switch which is kept off.

There is no other 'cylinder', like one in an airing cupboard, for instance.

So, what happens? Does the Megaflo heat the CH & HW water or does the gas flame in the Potterton? The water comes into the house off the mains, presumably passes through the Potterton, is heated then goes up to the Megaflo, then gets 'pressurised'? - and stored?

Do they mean, when they say that the Megaflo can heat up its tank of water in 30 mins that it means 'using the electric immersion'?

And- can or do you 'bleed' radiators in a sealed system?? I would think not!

Sorry about the simplistic nature of my question but I don't get it! I know how a pool chlorinator works, though!

 

[Chunkydoc]

In simplistic terms the Megaflow provides your hot water and the potterton provides your heat.

Someone much smarter than I will be along shortly to advise if the potterton is working with the megaflow. In older systems the boiler also heated the water in the HW storage tank, in your case the megaflow. I suspect it may be the case also but I'm not too familiar with how the megaflow system is configured.

 

[D_Hailsham]

Hope this diagram helps.

It's a very simplified version of an unvented system.

The water passing through the heat exchanger is heated up by the boiler flame. The heat is then pumped to the radiators and/or the Megaglo. In the Megaflo the reverse happens: the water passes though a coil where the heat is extracted to heat the water in the body of the cylinder, which is under mains pressure. When a tap is turned on the mains pressure forces the hot water out of the cylinder to the tap; it is replaced by cold water.

The control valves are motorized and are open and closed by the room and cylinder thermostats.

The electric switch, which is kept off, is for an electric immersion heater in the Megaflo; it is there as a standby in emergency if the boiler is not working. It will be much slower heating the water as the immersion only 3kW, while the boiler will have a much greater heat output.

Untitled

• D_Hailsham
• 2 Oct 2012
• 1

 

[dcawkwell]

The megaflow is a pressured tank of hot water for the hot taps.
It is heated by a copper coil of pipe inside the tank that the potterton boiler heats up. The potterton boiler will heat both the central heating
and the hot tank. Should the potterton boiler fail you will still be able to
heat the megaflow by using the immersion heater electric switch connected to the megaflow tank.

 

[D_Hailsham]

Yes, you can bleed the rads on an unvented system. The only difference from an open-vented system is that you have to remember to re-pressurise the system afterwards.

There will be a filling loop (usually a flexible pipe with a valve each end) near the boiler. When the valves are opened mains water will enter the system and the pressure gauge will show an increased pressure. When the correct pressure has been reached, turn off the valves.

Bleeding is best done when the system is cold; start with downstairs radiators.

The filling loop should be disconnected at one end when not in use. This is to prevent possible contamination of the incoming cold water by the water in the heating system.

 

[miljee]

Thanks very much. I and my bloke (who can program a mean computer but who can't hammer in a nail...) will study the diagram closely- there may be a couple more questions!- but thanks to everyone for helping!