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Can someone explain how my gs HW & CH system works please?!

(4 Posts)
Erebus Tue 02-Oct-12 10:40:01

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!

PigletJohn Tue 02-Oct-12 14:07:54

incoming cold water from the main goes into the megaflow, whenever a hot tap is opened allowing water out of the megaflow.

When the timer is "on" for HW, and the thermostat on the Megaflow feels cold, it "calls for heat".

The boiler receives this signal, and heats up, turns on the pump, and opens a motorised valve on the pipe to the cylinder. The pump sends hot water from the boiler, up this pipe, which is coiled round inside the cylinder. Heat passes through this copper coil into the fresh water in the cyllinder. The water in the boiler and coil does not mix with the water in the cylinder. It then returns to the boiler, is heated again, and repeats its journey until such time as the thermostat on the cylinder is satified and stops calling for heat. When the boiler is not receiving a call for heat it shuts dow. The water continues circulating for some minutes to absorb residual heat from the boiler.

When the timer is "on" for CH and the room thermostat feels cold, it calls for heat. The boiler receives this signal, heats up, turns on the pump, and opens either a different motorised valve allowing water to circulate through the radiators; or opens an additional port on the motorised valve if it is a "3 port valve."

If both CH and HW are calling for heat at the same time, the boiler usually circulates hot water through both of them, but can be set to give one or the other priority, for example if the boiler has insufficient power to heat both.

The Megaflow (or an ordinary cylinder if you have one) contains 100 litres or more of hot water, so there is no delay in obtaining hot water to run a bath or shower, and it can come out of the taps as fast as the main (or roof tank) can replenish it. This means that homes with a poor incoming water supply will have poor hot water out of the taps if you have a Megaflow. If you have poor supply, a cold water tank in the loft will usually hold enough water to fill a bath, and the tank can refil at its leisure.

A house with a poor mains supply can usually be improved if a new, larger pipe is laid between the house and the road. This may require tiresome excavation.

Yes, you can bleed radiators in a sealed system, but you will have to top up the pressure afterwards. It should not often be necessary if an inhibitor has been added and the water is clean, because it contains a limited amount of dissolved oxygen that will soon be used up in making the insides of the radiators rusty.

Erebus Tue 02-Oct-12 14:31:36

Ah ha! I get it now! Thanks!

minipie Tue 02-Oct-12 14:54:39

Thank you OP and PigletJohn, very useful to know! (we also have a Megaflow)

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