I need to drain our Megaflo to replace the immersion heater(s). The system
is a mains-fed one, ie no tank in the loft. I just want to check the
procedure for draining and re-filling the cylinder, please.

1. Turn off cold water feed.
2. Open hot tap and let as much water drain out as the air pressure thingy
inside the Megaflo expels.
3. Connect hose to drain and drain it.

Question: The Megaflo will need to fill with air when the water drains out.
Where does the air come from? Is there an automatic valve somewhere, or do I
need to open something? Or does it get sucked in through the open hot water
tap?

Filling:
1. Close drain valve, and open cold water feed.
2. Anything else???

Do these things come with an instruction book? If so, I have no idea where
ours is, assuming that the builders ever left it.

Thanks for your help.

"GB" wrote in message
...
I need to drain our Megaflo to replace the immersion heater(s). The system
is a mains-fed one, ie no tank in the loft. I just want to check the
procedure for draining and re-filling the cylinder, please.

1. Turn off cold water feed.
2. Open hot tap and let as much water drain out as the air pressure thingy
inside the Megaflo expels.
3. Connect hose to drain and drain it.

Question: The Megaflo will need to fill with air when the water drains
out.
Where does the air come from? Is there an automatic valve somewhere, or do
I
need to open something? Or does it get sucked in through the open hot
water
tap?

Filling:
1. Close drain valve, and open cold water feed.
2. Anything else???

Open hot tap and leave open until all air is expelled.

Do these things come with an instruction book? If so, I have no idea where
ours is, assuming that the builders ever left it.

Thanks for your help.

"Heliotrope Smith" wrote in message
...

Filling:
1. Close drain valve, and open cold water feed.
2. Anything else???

Open hot tap and leave open until all air is expelled.

Do these things come with an instruction book? If so, I have no idea
where
ours is, assuming that the builders ever left it.

Ah, many thanks! I eventually tracked down the installation manual, which
says this (just in case somebody else needs to know at some time in the
future):

8.4 DRAINING THE MEGAFLO UNIT

Switch off the electrical supply to the immersion heater(s) and shut down
the boiler on

indirect units. Turn off the mains water supply to the Megaflo unit. Attach
a hosepipe to the drain

cock having sufficient length to take water to a suitable discharge point
below the level of the unit, at

least one metre below the unit is recommended. Open hot water tap nearest to
the Megaflo to relieve

the system pressure. Open drain cock. If water fails to drain from the
Megaflo vent the unit by

manually opening the Temperature/Pressure Relief Valve.

8.5 DESCALING IMMERSION HEATER(S)

Open the cover(s) to the immersion heater housing(s) and disconnect wiring
from immersion heater(s).

Remove the thermostat by carefully pulling outwards from the immersion
heater. Unscrew immersion

heater backnut(s) and remove immersion heater from the unit. A key spanner
is supplied with the

Megaflo unit for easy removal/tightening of the immersion heater(s). Over
time the immersion heater

gasket may become stuck to the mating surface. To break the seal insert a
round bladed screwdriver into

one of the pockets on the immersion heater and gently lever up and down.

Carefully remove any scale from the surface of the element(s). DO NOT use a
sharp implement as

damage to the element surface could be caused. Ensure sealing surfaces are
clean and seals are

undamaged, if in doubt fit a new gasket.

Replace immersion heater(s) ensuring the lower (right angled) element hangs
vertically downwards

towards the base of the unit. It may be helpful to support the immersion
heater using a round bladed

screwdriver inserted into one of the thermostat pockets whilst the backnut
is tightened. Replace the

thermostat(s) by carefully plugging the two male spade terminations on the
underside of the thermostat

head into the corresponding terminations on the element.

Rewire the immersion heater(s) in accordance with Diagram 8. Close and
secure terminal cover(s).

8.6 REFILLING SYSTEM

DO NOT switch on the immersion heater(s) or boiler until the system has been
completely refilled.

Close the drain tap. With hot tap open, turn on mains water supply. When
water flows from the hot

tap allow to flow for a short while to purge air and to flush through any
disturbed particles. Close hot

tap and then open successive hot taps in system to purge any air. The
electrical supply can now be

switched on.

"GB" wrote in message
...
I need to drain our Megaflo to replace the immersion heater(s). The system
is a mains-fed one, ie no tank in the loft. I just want to check the
procedure for draining and re-filling the cylinder, please.

1. Turn off cold water feed.
2. Open hot tap and let as much water drain out as the air pressure thingy
inside the Megaflo expels.
3. Connect hose to drain and drain it.

That's right. The cold feed shutoff and pressure reducing valve are
usually located close by. Shut it. Open a hot tap untill the expansion
volume has exhausted, and the water stops flowing. This can take a
surprisingly long time! Time it to co-incide with a bath, so as not to waste
the hot water! Then, there ought to be a drain cock plumbed in just at the
cold feed, at the bottom of the cylinder ( colour-coded blue ring ).
Attach a hose, and drain down. Leaving the hot tap open will speed this up,
as air can enter this way. Otherwise, hold open the Temp / Pressure relief
valve ( directly above the cold inlet, grey colour-coded ring, cleary marked
as Temp /Pressure relief ) untill the gurgling stops and the cylinder is
empty.

Question: The Megaflo will need to fill with air when the water drains
out. Where does the air come from? Is there an automatic valve somewhere,
or do I need to open something? Or does it get sucked in through the open
hot water tap?

It will naturally fill with air during draining-down, either via the hot
tap, the manually opened T/P relief, or by air bubbling back up the drain
hose. Don't worry about it.

Filling:
1. Close drain valve, and open cold water feed.
2. Anything else???

No. This will re-generate the air volume too, which is something you need
to do occasionally ( anually here ) anyway, as per the instructions on the
front.

Do these things come with an instruction book? If so, I have no idea where
ours is, assuming that the builders ever left it.

Yes.
There's an installation manual in pdf format he
http://www.heatraesadia.com/hs/heatraes.nsf
I don't thhink there's a user manual, other than the instructions for
re-generating the air volume which is on a label on the cylinder. They
should have left a Benchmark Log Book ( service history, basically ) with
the installation.

Thanks for your help.


--
Ron

GB wrote:
I need to drain our Megaflo to replace the immersion heater(s). The system
is a mains-fed one, ie no tank in the loft. I just want to check the
procedure for draining and re-filling the cylinder, please.

1. Turn off cold water feed.
2. Open hot tap and let as much water drain out as the air pressure thingy
inside the Megaflo expels.

open cold tap elsewhere if the cylinder is high. That will drain it
pretty completely.
3. Connect hose to drain and drain it.

Question: The Megaflo will need to fill with air when the water drains out.
Where does the air come from? Is there an automatic valve somewhere, or do I
need to open something? Or does it get sucked in through the open hot water
tap?

Filling:
1. Close drain valve, and open cold water feed.
2. Anything else???

Do these things come with an instruction book? If so, I have no idea where
ours is, assuming that the builders ever left it.

Thanks for your help.

"The Natural Philosopher" wrote in message
...
GB wrote:
I need to drain our Megaflo to replace the immersion heater(s). The
system is a mains-fed one, ie no tank in the loft. I just want to check
the procedure for draining and re-filling the cylinder, please.

1. Turn off cold water feed.
2. Open hot tap and let as much water drain out as the air pressure
thingy inside the Megaflo expels.

open cold tap elsewhere if the cylinder is high. That will drain it pretty
completely.

No, it won't.

The hot draw-off is at the top.
The draw-off pipe extends some short distance down into the cylinder, to
allow for the expansinon volume.

Regardless of how low the tap is, it will only drain as far as the end of
the draw-off pipe, or untill the pressure in the expansion volume is
exhausted. This is not low enough to replace the immersion elements, which
are mounted on the side of the megaflo cylinder.

--
Ron

replying to GB, Terry Taylor wrote:
I have an unvented megaflow DD145HE in which I need to replace the bottom
heating element. I have good basic plumbing skills and a fully qualified
electrician to assist. Looking at this thread it seems fairly straightforward,
any reason why I should not tackle it?

--
for full context, visit https://www.homeownershub.com/uk-diy...er-419289-.htm

On Thu, 28 Sep 2017 13:44:02 GMT
Terry Taylor m wrote:

replying to GB, Terry Taylor wrote:
I have an unvented megaflow DD145HE in which I need to replace the
bottom heating element. I have good basic plumbing skills and a fully
qualified electrician to assist. Looking at this thread it seems
fairly straightforward, any reason why I should not tackle it?


Terry,

Did you find out if GB, posting in 2007, succeeded?

--
Davey.

On 28/09/2017 17:14, Davey wrote:
On Thu, 28 Sep 2017 13:44:02 GMT
Terry Taylor m wrote:

replying to GB, Terry Taylor wrote:
I have an unvented megaflow DD145HE in which I need to replace the
bottom heating element. I have good basic plumbing skills and a fully
qualified electrician to assist. Looking at this thread it seems
fairly straightforward, any reason why I should not tackle it?


Terry,

Did you find out if GB, posting in 2007, succeeded?


I did!!!!!!