central heating questions

[steve marchant]

Are there any rules of thumb for choosing the right size(capacity) of supply tank, and dimensions of the expansion pipe (which empties into the tank)?Appreciate some views on this.

[Andrew Gabriel]

If you're talking about the central heating expansion tank, then people choose to have sealed systems nowadays which don't have those components at all.

[Cicero]

================================== A header tank (expansion tank)for an open vented system seems to be quite standard at 4 gallons thus:

or:

The size of expansion pipe will be specified in the boiler installation manual (specifications) and for most domestic installations it will probably be 22mm rising in an arc about 18" above the header tank.

Cic.

[steve marchant]

sorry for not responding earlir - problems with the pc. Yes, i took a chance and installed a 4 gal tank with 22cm expansion pipe. Reason i put the questions was i found the feed (outlet) pipe, expansion pipe, and the water in the supply tank was getting quite hot. couldn't understand why this was happening and got alarmed..Shut the whole system down. Still trying to figure it out and have been unable to get any advice.

[Astral Voyager]

I had that once after a new system was installed. It turned out to be insufficient height of the expansion pipe. The head generated by the pump was pushing hot water up and out of the expansion pipe into the header tank. The system was thus losing water and drawing more in from the header tank. This meant that hot water was effectively circulating through the header tank. There was no overflow as it was effectively a self perpetuating cycle. Easily checked for - with the system running see if water is coming from the expansion pipe into the header tank.

Ours was fixed by increasing the height of the expansion pipe above the tank. Possibly also fixable by reducing the speed if you have a variable speed pump.

I'm in no way a central heating expert so you may get better suggestions.

Mel.

[steve marchant]

Thanks, Mel, reducing the pump speed seems to have done the trick.The temperature of the radiators has fallen some, but i'd sooner suffer the slight loss of efficiency than have the tank soften and leak.