DIY Doctor

hot water cylinder replaced - some questions

Postby chrisw99 » Tue Nov 06, 2007 8:51 am

I recently had the hot water cylinder replaced in an indirect gravity fed system. At first it didn't work due to a massive air lock, but when I cracked open the nut on the flow inlet it all started working.

Some questions..

The hot water pipe from the boiler comes up to a T junction.. one way goes up the vent, the other went horizontal into the old cylinder. because the entry point is a few inches higher on the new cylinder, a couple of 90 degree bends have been put in. I have been finding the return pipe getting steadily colder as the days go by, so I crack open the nut again on the inlet pipe - some air spurts out, and then the return pipe goes immediately hot again.
I've been doing this about once a week in the 5 weeks since the new cylinder... is this just residual air in the system from when it was replaced and eventually there'll be none left, or is air getting in? on the old system, due to that T junction, any air building up there would have been able to get up the vent but with the new raised bit it's stuck.

Also, when everything is switched off, if I place my ear to the top of the cylinder i can hear a water trickling noise every few seconds. As no water is moving about when everything is switched off, what could this noise be?

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Simply Build It

Postby htg engineer » Tue Nov 06, 2007 9:07 pm

Where you have put the 90 degree bends in this is the ideal place where air will become trapped, you's be piping up the new cylinder the same as the old, cut out the tee piece and add a connector, add the tee piece further up where it will be horizontal with the cylinder connection (like the old one). You need to keep bends to a minimum for it to work properly.

For example one bend off the boiler, one bend into the cylinder. If possiblt.

You will hear water trickiling if there's air in the boiler, once the pipes, boiler and coil are FULL of water - the water can then only circulate, not run. Hope you undertstand this/makes sense.
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Postby chrisw99 » Thu Nov 08, 2007 1:36 pm

Thanks for the response htg, I shall get the plumber back in to raise the T to the vent/cylinder so that it is level with the cylinder entry point.

The other question - is this just residual air from when the cylinder was replaced, or should that have gone the first few times i opened the nut to let some out? In which case air is getting in somehow?

I tried an experiment I read on here.. I placed the expansion vent in the loft in a pint glass of water and watched when the heating came on. The level dipped about an inch, then went back up followed by a good spurt of air. Is this normal/good/bad??
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