Leaky valve

[tabita]

Hi,

My boiler is a Heatrae Sadia Megaflow. The problem is, the valve leaks if I leave the boiler on for 2hours. It will keep on leaking until all the hot water's gone! However, no problem if I on the boiler for just 1hour.
i dunno if there's enough details, but please help.

 

[JPC]

and i thought they were uhw cylinders

 

[tabita]

well, I don't know what a uhw cylinders are, but let me try showing what i meant in this picture.
www.gasapplianceguide.co.uk/Systemfit_03_1.jpg
If I can just pinpoint it right, I'm saying the "diamond shaped, black thing, connected on one end, on the right of the picture" leaks. Now, i don't know what to call it except valve. What's the proper term for it?

 

[scatmanjohn]

Hi...the diamond shaped thing is called a tundish. When you see water dripping out of it put your finger under it and let us know if it is hot or cold water dripping.

 

[tabita]

haha, so the tundish thing. I haven't actually felt the water directly. But i've felt the pipe that was leading to the tundish. It was hot when dripping. And the one time when i try feeling again after it's stopped dripping, it was COLD.

 

[chrishutt]

Sounds like you've lost your air bubble! The Megaflo has an internal air bubble which absorbs expansion of heated water. Over time the air bubble is absorbed by the water and needs to be restored.

I think you do this by closing the cold inlet valve, running off the hot water from a tap, then opening the cold water inlet valve. But don't attempt it until you are sure which valve is which, because you don't want to fiddle with the wrong valves on unvented cylinders (please, it's not a boiler).

 

[tabita]

Running off the hot water? Do i need to run the water until there's no hot water left, before opening the cold water again?
And dont' attempt it? why not? which valve if i get wrong will cause disaster in the cylinder?

 

[chrishutt]

As I said, I'm not sure of the procedure with Megafloes, so either wait for someone else to say for sure, or do a search on Megaflo air bubble say, and look through some other threads on this.

I've found this for you. Go to products, then Megaflo, then download the installation instructions and look at page 26.

 

[Gasman1015]

The procedure is correct, however you may want to read here about other causes of your problem.

http://www.heatraesadia.com/HS/HeatraeS.nsf/FaultDiagnosis_b

 

[chrishutt]

Actually the procedure I first described was not complete. After opening the lowest hot tap you should open the Temperature Relief Valve to allow the air in. This requires an awareness of which valve is which.

 

[alexp.1]

There should be a big sticker on the cylinder telling you how to recharge the air bubble.

 

[tabita]

ah, the big sticker. I'm sure i've followed that step before. it uses the term "overflow" instead of tundish!? anyway, I carried out the instruction, and halfway through it, it says "hold temp/pressure relief valve until gurgling stops and water stops running from valve and tap". This time, I held the pressure relief valve for 2minutes and it still haven't stop gurgling. I can still hear bubbles from the cylinder. out of fear of over replenishing the air bubble and exploding it, i just stopped at 2minutes....
any ideas if this is ok, before I switch it on?

 

[chrishutt]

it says "hold temp/pressure relief valve ...." ....... I held the pressure relief valve for 2minutes

That's a different valve. Try following the instructions.

 

[tabita]

oh dear, I can't find any other prospective valves. The one that i was twisting has a label of "set temp 90-95, set pressure 10bar, discharge 10kW, date". Other valves include a 3bar (which i can't budge), and a 8bar.
am i twisting the wrong valve?

 

[chrishutt]

You were opening the right valve, the temperature and pressure relief valve, but you called it something else in your post. Just me being pedantic really.

To answer your question, if the water kept running, are you sure you turned off the cold water supply valve? Anyway, the thing to do is just to try it out. Either you'll still have the problem, or most likely you wont.

By the way, unvented cylinders need "servicing" from time to time, in the same way as boilers, just to make sure that they're safe to use. The person doing the servicing should have an "unvented ticket" or qualification.