How to Replenish Air Gap In Unvented Cylinder?

AOIS · Sep 7, 2019

I have noticed water dropping intro the tundish of my Megaflo Unvented cylinder. I believe I need to replenish the air gap.

Do I need to switch both the levers/valves off in the pictures attached before starting the process?

Thanks in advance.

chris watkins · Sep 7, 2019

AOIS said:
I have noticed water dropping intro the tundish of my Megaflo Unvented cylinder. I believe I need to replenish the air gap.

Do I need to switch both the levers/valves off in the pictures attached before starting the process?

Thanks in advance.

If you are not sure turn the small one off (across the pipe) under the pressure reducing valve.
but it should just be the the one labelled "cold water mains isolation to hot water cylinder".

Open the hot taps (lowest one such as bath) wait until the water stops running then twist the T&P knob, if your cleaver you might get it balance in the open position before it clicks over on the cam, if not you will need to hold it. This will allow the air in & the water out of the tap . You may need to keep this going for 10-15 mins until the water stops running & the air gluging-in.
Turn T&P to closed, shut hot taps, open up the isolation valve refill the system, open hot taps to vent the air in the pipes.

Most important dry out the tun-dish & check that water has stopped dripping & again in a day of 2, if it is still wet after two days then you will need to call an Un-vented plumber to check over the system.

AOIS · Sep 7, 2019

chris watkins said:
If you are not sure turn the small one off (across the pipe) under the pressure reducing valve.
but it should just be the the one labelled "cold water mains isolation to hot water cylinder".

Open the hot taps (lowest one such as bath) wait until the water stops running then twist the T&P knob, if your cleaver you might get it balance in the open position before it clicks over on the cam, if not you will need to hold it. This will allow the air in & the water out of the tap . You may need to keep this going for 10-15 mins until the water stops running & the air gluging-in.
Turn T&P to closed, shut hot taps, open up the isolation valve refill the system, open hot taps to vent the air in the pipes.

Most important dry out the tun-dish & check that water has stopped dripping & again in a day of 2, if it is still wet after two days then you will need to call an Un-vented plumber to check over the system.

Thanks Chris. So just this one in the picture then?
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I have given it a go. Not sure if I fully completed the process correctly though but made sure that all hot water had stopped flowing from the downstairs open hot water tap before turning the cold water valve back on by the cylinder. There was rush of pressure when this happened, I presume this is normal? After about 10 seconds this stopped. I have turned some taps on around the house and no issues with pressure. During the whole process there was very little water flowing through the tundish.

Is it possible to do this process wrong and cause other problems or will it just solve the issue?

Thanks

chris watkins · Sep 7, 2019

AOIS said:
Thanks Chris. So just this one in the picture then?
[automerge]1567859226[/automerge]
I have given it a go. Not sure if I fully completed the process correctly though but made sure that all hot water had stopped flowing from the downstairs open hot water tap before turning the cold water valve back on by the cylinder. There was rush of pressure when this happened, I presume this is normal? After about 10 seconds this stopped. I have turned some taps on around the house and no issues with pressure. During the whole process there was very little water flowing through the tundish.

Is it possible to do this process wrong and cause other problems or will it just solve the issue?

Thanks

Did you open up the T&P safety valve this is the fitting screwed into the side of the cylinder, on the right hand side, close to the top. Did you hear the air going in? as it went in the water would have come out of the downstairs hot tap, if the bubble was completely lost it would likely take a min of 10 - 15mins for all the water to drain & be replaced with air.
If you didn't get all of the above then yes it is likely you got it wrong, still not a problem just repeat the process again tomorrow.

Chuck · Sep 8, 2019

AOIS said:
There was rush of pressure when this happened, I presume this is normal? After about 10 seconds this stopped.

The outflow via the tundish stops after about 10s but that's the start of the process not the finish! You need to keep the valve open for ca 15 minutes while your lovely hot water runs down the drain via the tap hot tap you have opened, which should be at a height below the tank.

The valve has a strong spring on and rather sharp knurling so, unless you have "plumber's fingers", wear a glove. You're done when you start hearing a gurgling sound inside the tank.

You can get a feel for the state of the air bubble by briskly running off a few litres of HW, shutting the tap and listening carefully. If your air space is full you will hear CW filling for about 10s as the buble compresses. As the air space gets depleted this period gets progressively shorter.

AOIS · Sep 8, 2019

Thanks for your help both. I don’t think I held the value open for long enough, I found finding the correct position to keep the value open difficult, it kept clicking closed again. It looks like I have carried out the process correctly but just need to keep the value open longer until the gurgling stops and the water stops running downstairs.

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How to Replenish Air Gap In Unvented Cylinder?

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