Megaflo and combi boiler

Kemik · 12 Sep 2017 at 19:53

Hi guys,

This is going to make me sound like an absolute idiot but happy to take one for the team...

Just moved into a New Build. It has:

a condensing boiler,
two zoned thermostats with timers for high, medium, and low temperature,
radiators with TRVs except the two zones, and
a megaflo system (eco unvented indirect cylinder)

How the hell does this system work?

At first I thought each floor of the house was controlled by the thermostats. Heating would only come on when they called for heat. The TRVs would only allow hot water into the radiator when the dedicated thermostat requested it and the temperature was below the room TRV temperature.

Until... I found another single timer in the boiler cupboard. It says "CH", which to me would mean central heating. I called the house builder and asked what it was for. They called the plumbers and told me "it's for the hot water. Leave it on all of the time". What? What is the point in a timer for hot water if I need to leave it on? I have always had hot water since I moved in but the timer is showing as off... so how does that work?

Then, I opened the megaflo cupboard and saw an electric switch on the wall is on. What is the switch for? What is the megaflo for? Have I been using electricity to power my hot water rather than gas? I don't think so because when all of the thermostats are off and I turn on a tap, the boiler kicks in.

Surely making a nuclear bomb is less complicated than this stupid system??

robj20 · 12 Sep 2017 at 20:10

Sounds like the ch in the cupboard controls the heating up of the megaflow. Usually when done like this the megaflow supply the bathroom and the combi hot water basins and kitchen.

Participant · 12 Sep 2017 at 20:17

The switch in the megaflo cupboard could be an immersion heater.

rexehuk · 12 Sep 2017 at 21:26

I'm jealous you have a megaflo

Kemik · 12 Sep 2017 at 21:40

robj20 said:
Sounds like the ch in the cupboard controls the heating up of the megaflow. Usually when done like this the megaflow supply the bathroom and the combi hot water basins and kitchen.

But we've had hot water with the timer being off.

Participant said:
The switch in the megaflo cupboard could be an immersion heater.

I'm really hoping this doesn't mean our hot water has been heated by electricity... The boiler seems to kick in when I switch on a tap too.

robj20 · 13 Sep 2017 at 07:02

Kemik said:
But we've had hot water with the timer being off.

I'm really hoping this doesn't mean our hot water has been heated by electricity... The boiler seems to kick in when I switch on a tap too.

Do all hot water taps fire up the boiler, including any electrical showers? If you had read my post i said the common way of doing it (not that having stored hot water with a combi is common) is having the bathroom or even just the bath and shower fed by the cylinder, all other taps via the DHW of the combi.
Figure that out and you have your answers.

Next would be to find out what the switch is, to find that out if the bath or shower does use the cylinder, run it for a while to deplete the cylinder and see if the boiler fires up to heat it back up, or check your electric meter to see if it spins like crazy to heat it up.

psd99 · 13 Sep 2017 at 08:37

megaflo in a NEW BUILD!? You lucky sod!

Bet it is built with plasterboard absolutely everywhere tho

Kemik · 13 Sep 2017 at 09:39

robj20 said:
Do all hot water taps fire up the boiler, including any electrical showers? If you had read my post i said the common way of doing it (not that having stored hot water with a combi is common) is having the bathroom or even just the bath and shower fed by the cylinder, all other taps via the DHW of the combi.
Figure that out and you have your answers.

Next would be to find out what the switch is, to find that out if the bath or shower does use the cylinder, run it for a while to deplete the cylinder and see if the boiler fires up to heat it back up, or check your electric meter to see if it spins like crazy to heat it up.

Ah sorry, I mis-read. Will try that out tonight.

TripleT · 13 Sep 2017 at 13:06

I'm buying a new build with a megaflo and during the home demo (lol?) they said that the switch near the mageflow should always be off... As that's when it heats the water via electricity as you suspect.

I'm sure we have a digital timer near the Combi for setting the heating. It doesn't work how you suspected based on the thermostats afaik, that would be a bit mental.

The mageflo just puts the hot water under pressure as far as I can remember, meaning great showers.

Mr.Stu · 13 Sep 2017 at 13:27

TripleT said:
The mageflo just puts the hot water under pressure as far as I can remember, meaning great showers.

Megaflo, or any other non vented cylinder, uses the pressure of mains cold to force out the hot water! This is typically reduced to 3bar via a valve before entering the cylinder. Same pressure on cold and hot, so works a treat. But as with pumped mavity systems, just need to make sure your cylinder has a big enough capacity to cater for your showering needs.

Just make sure you keep on top of the annual servicing that includes renewing an air pocket internally that is used for pressure control (as there is no vent pipe, as in a traditional system).

robj20 · 13 Sep 2017 at 13:54

TripleT said:
I'm buying a new build with a megaflo and during the home demo (lol?) they said that the switch near the mageflow should always be off... As that's when it heats the water via electricity as you suspect.

I'm sure we have a digital timer near the Combi for setting the heating. It doesn't work how you suspected based on the thermostats afaik, that would be a bit mental.

The mageflo just puts the hot water under pressure as far as I can remember, meaning great showers.

Is yours also run via a combi boiler. Normally they are run from a conventional or system boiler.

Kemik · 13 Sep 2017 at 14:14

TripleT said:
I'm buying a new build with a megaflo and during the home demo (lol?) they said that the switch near the mageflow should always be off... As that's when it heats the water via electricity as you suspect.

I'm sure we have a digital timer near the Combi for setting the heating. It doesn't work how you suspected based on the thermostats afaik, that would be a bit mental.

The mageflo just puts the hot water under pressure as far as I can remember, meaning great showers.

Yeah, I suspect that is what we have been doing. It was switched on when we moved in so I never challenged it in case the Megaflo needed it to work! As soon as the builders confirm this I'll be asking them for ££ to cover it.

What is the point of the timer on the thermostats if they need a timer near the boiler too?

TripleT · 13 Sep 2017 at 15:36

robj20 said:
Is yours also run via a combi boiler. Normally they are run from a conventional or system boiler.

Yer run off a combi boiler.

Kemik said:
Yeah, I suspect that is what we have been doing. It was switched on when we moved in so I never challenged it in case the Megaflo needed it to work! As soon as the builders confirm this I'll be asking them for ££ to cover it.

What is the point of the timer on the thermostats if they need a timer near the boiler too?

Sorry I didn't see that your thermostats were timed so ignore that! Apologies. I thought you were expecting something like climate control where you set the (non timed) thermostat to a temp and it just flicked on and off to maintain that temp so effectively on all the time.