Filling up gravity central heating

Airlock.

No CH when I was a kid, but a routine at home every time a hot water tap washer had to be changed was to connect a hose between hot and cold water taps in the bathroom, and turn both on.

I don't suppose that was a cottage in Southwold?:-)

Congealed sludge in the downfeed from the header? I had that a few years ago on a bend situated behind the hot water tank. Happy days.

except that both those taps would be fed from the same tank so should have equal pressure.

Connecting the kitchen cold tap fed from incoming mains to a hot tap would be more like it.

especially since the blockage might have suddenly released when the valve was removed :-)

varies (by region?) ... no cold tap in this house is fed from the tank

The HW tank is not relevant is it?

I never touched it.

Doesn't work with the header tank, though.

In that case try connecting a hosepipe to the C/H drain c*ck, and see if that pushes water up into the C/H header tank ?.

You might have to manually move the 3W valve to the heating position.

There is usually (always?) a manual lever on the valve which allows both sides to be open and latched to facilitate filling. The latch on the manual lever should be overriden when the system is in operation by first switching to CH and then hot water only.

Gunged up T-Junction, where the feed pipe from the header tank joins the main heating pipework.

Mike

Mine did, as we were moving a full HW cylinder ;-)

Owain

Hi Adam,

I'm confused! Which bit is gravity? If there's a mid-position valve, the primary circuit is presumably fully pumped. It may be vented (as opposed to pressurised) if there's a small fill and expansion tank - but that doesn't make it "gravity". Is it thins tank which you're referring to as the header tank, or do you mean the large cold water header for the (presumably) gravity HW system?

Can you clarify just what you mean by "won't fill back up". Exactly what is happening or not happening?

As someone else has pointed out, the 3-way valve will be in the HW-only position when no power is applies to it. The manual lever moves it to the mid position, when you should get some flow to both circuits. You may need to do that if the primary circuit won't refill properly.

If there is a pump, make sure that there is water in it by opening the bleed screw and then apply power.

Also bleed radiators.

That only worked if the cold was from the mains. Brian

Indeed a well tested solution, but worth mentioning that will clear an airlock in a vented hot water system, it won't help when there is one in the vented CH primary. You would need to find a way to connect your cold water tap to a rad tail or similar to have the same effect there.

Some crap getting sucked into the feed/expansion pipe connecting to the CH header would be one possibility.

Should have added, that a wet'n'dry vac hose held under water and over the outlet of the CH tank, might be worth a shot to see if you can suck some water back. Failing that, a hose stuffed down it, might fors some water though.

There may also be a bleed in the high point of the hot water system. Mine had an auto bleed valve but the screw on cover was tightly on thus only allowing a limited amount of air to escape until the cover was unscrewed.