Draining Pressurised Central Heating

[sherbo]

I've recently had my gas central heating system switched over to a sealed/pressurised with an expansion vessel taking a feed from the main. But when I'm draining the system (attaching hose to drainage valve and opening fully), it doesn't drain properly - the water continuusly flows out of it. It's as if there's another, secondary water supply going into my heating system. Yesterday I even knocked off the water at the main stopcock so the vessel and the sealed system didn't get a feed, but the water was continuously draining out of the hose (I mean for over 12 hours). In the end I had to just close the drainage valve. Any advice gratefully received.

[adder1969]

Is this for real? if so , what does the pressure gauge reach if you fill it from the mains, does it go up and up and up or reach a (low) level then stop?

12 hours of draining even if there was still a feed from a large header tank, with the mains switched off, seems like something very odd is going on!

[sherbo]

Yep - I'm afraid it is for real. When the system's filled and working the pressure continually drops to 0. I fill the expansion vessel up to

1bar then it drops steadily to 0 again (over about 3 minutes - quicker if I have hot water AND heating on). I'm 99% certain there are no leaks - the house has a basement on the ground floor so I can see all the pipework - if there is a leak it would have to be under the kitchen's concrete floor, but there are no visible signs on the concrete or outside. The pressurising has been done by a good, qualified plumber, but he's running out of ideas and I'm thinking I'll have to get a second opinion during Christmas week :-(

[Pete Cross]

If you turn the stopcock off, can you still run water from the cold taps ? faulty stopcock ? or..... in our house the old cast iron water main ran along the back of the house and entered in the kitchen with a stop tap. Later a new plastic main was routed past the front and now enters under the drive and into the front, they simply turned off the rear stop tap and put a warning label over it. If that old feed is still 'live' and we turn off the front stop tap, there could be some water entering by the old route ?

Pete

[adder1969]

Sounds like the header tank is still connected!? ...or, there's a leak in your HWC which means the tap water and heating are mixing. but that wouldn't lead to constant 12 hour running water with the stopcoc off.

[vortex2]

Do you have indirect hot water?

If yes it could be a leak in the heat exchanger.

David

[sherbo]

Pete,

Thanks for the response. With the stopcock off the cold taps run dry (once the tank in the attic drains) - not even a drop comes out. What you have said is entirely plausible - a secondary supply would account for the pressure dropping as well as the never-ending draining. The supply with the stopcock appears to be the original (house is 100 years old and the main is a lead pipe)...

[Ed Sirett]

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