Megaflo System (20 chars)

[Pickles]

We bought a new build a few years ago with a Megaflo system, but I've long wondered how it worked and have now decided to ask.

I get that there's a coil in it off the boiler, and also an immersion. But it's the immersion I have trouble understanding. There's no controls for the immersion, just a simple (Myson) timer in the kitchen which tells when to call for hot water.

The only way I can think this would be wired so that the immersion works automatically is as follows:

1) If there's a call for HW while the CH is on, a valve is opened allowing the hot water in the CH pipes to also flow through the coil in the tank
2) If there's a call for HW while the CH is off, the valve remains closed and instead the immersion springs in to action.

So that's why I'm here, would that typically be how it's wired? If that's the case it would mean hot water would mostly be produced by the boiler in the winter, and mostly by the immersion in the summer?

 

[steadyon]

Highly unlikely that the coil and immersion heater are directly linked.

However, there will be a thermostat inside the tank controlling the hot water temperature from the coil, which will turn the hot water supply from the boiler off when the tank temperature reaches the set point.

There will also be a thermostat with the immersion heater. Once the hot water temperature reaches that set for the immersion heater, the immersion will be switched off.

If the immersion thermostat is set for, say 65 degrees, and the coil thermostat for 60 degrees, if both immersion and boiler are on, the boiler will be switched off once the water reaches 60 degrees, but water will continue to be heated by the immersion heater until it reaches 65 degrees.

 

[Pickles]

So you say the immersion is used alongside the boiler to heat quicker, and then maybe as a topup (for that last 5 degrees or so)?

 

[steadyon]

No. Heating with gas is about a third of the cost compared with electricity. Leave immersion switched off and use only in emergency if the boiler breaks down. Depending on usage pattern, it may be cheaper to run immersion only in the summer when the boiler is otherwise switched off. Its a fairly simple calculation dependent on hot water usage volume and time to heat a tank full of water.

Above assumes gas boiler, not LPG , oil or other.

 

[Pickles]

Yes, but there's absolutely no controls to disable the immersion, I fear I'm going to need to look in to the wiring centre to see how it's all cobbled together.

 

[doitmyself]

The immersion heater is there as a standby, in case the boiler packs up.

You should find two motorized valves near the HW cylinder. One controls the flow of water through the rads; the other, the flow through the coil in the cylinder. When the water in the cylinder needs heating (a thermostat in the cylinder will have closed) the HW valve will open and the boiler will start. When the cylinder water is hot enough (usually 60C) the thermostat will open, the valve close and the boiler turn off.

A similar process happens with the central heating valve, which is controlled by the wall mounted thermostat - usually in the hall.

You will also have a timer/programmer which controls the times when heating and hot water can be on. (It may be a programmable thermostat for the CH).

 

[Pickles]

How would the immersion know to click in though? It must be wired through the rest of the CH/HW system in some way to know when it is needed

 

[Stigster]

Yes, but there's absolutely no controls to disable the immersion, I fear I'm going to need to look in to the wiring centre to see how it's all cobbled together.

Your immersion should be wired into a switched fused spur (like a light switch but with its own fuse inside the switch cover plate) and this is where you would switch it off. I've never come across an immersion heater wired into the wiring centre before. The most complexity I've seen that it is also on a simple timer, usually when there is no boiler in the property. As Steadyon says, most people would heat their water with their boiler and only use the immersion if the boiler breaks down. If the boiler does break down and the immersion is a few years old it has a 50/50 chance of actually working in my experience. I'm not saying immersion heaters are bad, far from it but they do fail every few years, especially if the water is a bit corrosive, the outer casing of the heating element corrodes and makes an earth fault.

 

[Pickles]

Your immersion should be wired into a switched fused spur (like a light switch but with its own fuse inside the switch cover plate) and this is where you would switch it off.

At the risk of repeating myself...

Yes, but there's absolutely no controls to disable the immersion, I fear I'm going to need to look in to the wiring centre to see how it's all cobbled together.

I'll let it boil over (pun intended) until it starts to annoy me enough that I can be bothered to take a look in the wiring centre and see what's going on.

Thanks

 

[Best]

Careful touching your wiring centre as there is permanent live wires there! It would need safely isolated.
As said above, your immersion MUST have a thermostat control (which includes a safety overheat cut out) at cylinder and an isolator switch nearby. If it doesn't have both, then get a G3 qualified plumber to look at it all because it is an unvented unit and a thermostat is a major safety control. You should have been getting that unit serviced once every year and any faults would be found. They are potentially dangerous and overheat is the biggest danger. Why not ask your plumber if you have any concerns?
Electricity is much more expensive than gas or oil to heat water and only use that immersion as an emergency - if your gas boiler was broke down etc

 

[king of pipes]

Post some pictures and i am sure one of us can advise you its hard to say untill you have seen what you have cheers kop

 

[SimonG]

Immersion should have local electrical isolation. I.e fused spur.

 

[Best]

Immersion should have local electrical isolation. I.e fused spur.

Apparently not a 13amp fused switch but just 20amp 2 pole switch as 3kw is on limit of 13amp switches.
It was mentioned to me on another thread.
I have noticed the 13amp switches burn out.

 

[ShaunCorbs]

Apparently not a 13amp fused switch but just 20amp 2 pole switch as 3kw is on limit of 13amp switches.
It was mentioned to me on another thread.
I have noticed the 13amp switches burn out.

Correct and normally a direct feed from the consumer unit, can be off the ring but depends what system you have