DIY Doctor UK DIY Forums

Just moving into a new house and doing some prep work on electrical and gas supplies. I've discovered that the gas boiler is a heat-only model for just central heating (that's fine for now) and it has a dual element MegaFlo hot water tank that is immersion-only (also fine for now).

It has two switches to operate the two tank elements and no timer. They are labelled as 'Heatwise' and 'Boost'. I had an identical Megaflo system at my old flat (new build) but it was properly wired into a Horstmann Economy 7 timer. I've bought the same timer for this installation with the view to changing it.

I have inspected the electric meter (Eon) and it seems to have three 'meters' (photos attached) when cycling through the screens: R1 (it flashes and I missed the actual '1' from the screenshot), R4 and T (total?). Anyone know what this means? I expected to see two rates (R1 and R2), one for Economy 7 (during the night only) and one for regular rate. I'm guessing Heatwise was some kind of other multi-time cheap rate electric meter type?

There also seems to be two live feeds from the meter to the house. Is this normal? Is it likely that the Heatwise switch is actually on a separate wiring circuit that only becomes active during the cheap rate hours or is it more likely that the meter just switches between the two rates, as per my old flat installation and the timer handles ensuring the night rate element only comes on during cheap rate hours?

Economy 7 is a tariff not a system and there are many systems using this tariff. Maybe some one will recognise the meter but as an electrician I have scratched my head a few times to try and work out what system in installed.

The older systems had completely different wiring for off peak to rest of the electrics often with a dedicated fuse box but this did not allow the washing machine, tumble drier etc to use the off peak power and latter systems instead of the DNO switching the power on and off it just noted time when power was used and the items within the house had their own timers.

With the older system often two immersion heaters were used one low down on the off peak and one higher up the tank on a boost switch which would work at all times. But this was not required with the newer system the same immersion heater worked normal and boost.

The megaflow tank also comes with many different flavours with different numbers of hot coils and immersion heaters in some cases the central heating is powered from the megaflow heat store allowing solar, wood burning and electric power all to be used to heat the radiators and because the insulation is so good unlike the brick radiator system heat could be stored for over a week when central heating was not required. The tanks however are rather large.

In my area not many flats most council owned so I have never worked on them. You may be lucky and find some one has worked on the system you show but likely you will need to re-post on one of the major forums like DIYnot where you will likely also get some abuse as not as well controlled as this one. But there are many more electricians using the forum who sling abuse at each other on a regular basis but in the end you may get your answer.

Ah ok, that's quite useful, Ta.

The house was built in 1999 and I've checked the fuse box, there doesn't appear to be any circuits marked for Heatwise-only.

Ah, the plot thickens.

There is actually a separate, smaller consumer unit with a single trip switch for the main immersion element, which I reckon runs off that second live feed from the electric meter.

Might have to ring the current supplier when I move in and find out how to go about wiring it up a bit better.

Looking at the second picture overall view of the meter there seems to be two supplies out one with one cable tie and the other with two cable ties so one would expect to find two consumer units one supplied from each output so one would have power at all times the other only when within the 7 hours of the cheap tariff.

One would expect to find two independent immersion heaters the upper being supplied all the time with the isolator fused connection unit called boost and the other lower down and likely set to a higher temperature to the FCU marked Heatwise but without tracing this is just a guess.

From what I can see it would seem your meter does the timing and there is no need for you to fit one. Normally you would leave the boost switch off at all times and the Heatwise on at all times except where you have used that much water that it has run cold.

Yeah, that sounds exactly right and definitely more than likely.

I'll see what the current energy company say on Friday when I move in. There are definitely 2 consumer units and the second is marked as the off-peak immersion element, which as you say probably has different temp settings.