Megaflo air gap replenishing

20 Jun 2013
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United Kingdom
Hello everyone,
I have a megaflo hot water cylinder which is dripping from the tundish. Have had two weeks ago a gas safe registered engineer to service my boiler and my hot water tank and he said the hot water cylinder would just need the air gap replenished (which he supposedly did).

However after a couple of days of his service water started to drop from the tundish again.

I have now decided to try replenishing the air gap myself. However when I turn off the mains or the inlet on the cylinder and then open the lowest hot water tap, no water is coming out of the hot water tap. Needless to say the cylinder is full.

Can you please give me some indications on what might be wrong?


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Could be a few things, you may have a defective pressure/temp relief valve. Sometimes these do not seat correctly after testing (servicing)

What is the pressure like from your hot taps?

You need to isolate the water turn on the lowest hot water tap then hold open the temperature/pressure relief valve until the cylinder stop gurgling and water stops flowing from the tap. Then turn the temp/pressure relief valve until it clunks shut, turn off the tap and the cold water back on to the cylinder just follow the instruction on the side of the cylinder
In no way is this a DIY job. You can't mess around with an unvented cylinder!!
You need a Plumber with a G3 unvented ticket.
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In no way is this a DIY job. You can't mess around with an unvented cylinder!!
You need a Plumber with a G3 unvented ticket.
With respect Richard. Megaflow have Users instructions on the side telling end user how to replenish expansion bubble.
Sorry, you maybe right Jeff, as there's a video on Utube showing the hard of thinking how it's done...... :oops:
These units need to be drained completely in order to replenish 'air gap' , if water temp is in excess of 60c then unit will require a drain down more frequently , if water stops flowing from hot tap when unit is issolated then obviously air gap has been depleted and unit will discharge water from TPR valve when heated.

If internal disc (flying saucer) has been dislodged then frequent replenishing will be required.

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