Nothing to do with bikes but sure there are some friendly biking plumbers on here!

Here it goes… Installed my ch 6 years ago. New boiler, tank pipework. Open system. Worked great.

Started to get a bit noisy so drained and filled with x800 for a week.

Today I had the joy of draining, flushing through and refilling.

Great….

All good. Apart from one rad… Downstairs. Rad get hot lovely all the way to the top…. But when I open bleed screw I hear air hissing. Weird thing is…. As I said…. Its boiling hot. All the way up to top both sides. So why the hell is water not coming out of the bleed nipple??

Open system with pump. No leaks. All rads hot….

Other thing I have noticed is the 15mm cold water feed from header gets pretty toasty (I am putting this down to expansion of hot water in the system)

Hmmmm bit of a loss on this one… Anyone have any ideas?

Are you bleeding it with the pump on? If so, don’t, as your pulling air in rather than venting it out.

What he sed.

Exactly what I was about to say.

IANAP.

15mm pipe from the header?
It should be 22mm. And shouldnt be getting warm much above the cylinder.
Is the pump puming too fast causing over-pump into the header tank?

Ta… No not pump on. Using our friend gravity.

It’s not pulling… It’s pushing (filling g up a balloon)

150 mm between 22mm expansion and feed (15mm)…think that’s all good.

Confused. Com

Try lighting the air/gas coming out of the bleed nipple.

Good shout flux…. Nope no hydrogen. Would be surprised as system is very very clean.

Left system overnight with bleed nipple cracked a tad… Still hissing this morning.

Turned heating on and system works great…. All rads get hot quickly. Even the one that seems to have an air pump in!

Still confused. Com

Snake trapped in the rad..

Try shutting down all the rads apart from this one and run it for a while.
could have a partial air lock feeding it and you aren’t clearing all the air hence the continual bleeding.
Radiator will still have some heat even with air in it.

Is the 150mm between the cold feed and open vent connections? If so then it is a maximum of 150mm. Both tees should be 22mm minimum and taken off a horizontal section, ‘not the normal rugby post’ set up that most people do to save 2 elbows.

Bear thanks. Pic below. This was part of the original install that I reused. One on left is vent (22mm) one on right is feed (15mm).

The feed is hot all the way up to the expansion tank (sticking my hand in I can feel hot water at the bottom) . I guess due to the smaller bore, water is expanding all the way up this one when it heats up. Vent is cold to the touch above a height of 1m.

Currently running the system on max speed with the one rad downstairs on as crofts suggest. Snake still in there…….

More like 100 mm between the two btw

Max speed can cause cavitation and potentially create air in the system.
Try it at setting 2 instead of 3. The air will have more chance of being sent to the expansion tank then.

Crofts thanks…. Only running on speed 3 to try clear the snake. Normal setting is 2. Still does it on 1.

I bet if I swapped the feed to 22 mm then the issue would go away.

It’s not pumping over (through the vent) but I guess there is quite a bit of expansion going on when water gets hot.

I guess as the 15 mm is smaller bore, expansion would move a larger distance of water if that makes sense.

vent bocked?

Doesn’t have to be a dirty system for there to be hydrogen present. Have you used any plastic pipe work in the system? Has the inlet been blocked at somepoint judging by the speedfit coupling?

Only plastic is on shower pump and that speed fit. Yeah it was blocked a bit when I installed circuit upstairs…. So hacked a bit off…and cleaned out with coat hanger.

Should have looked at this first. Just grabbed a novelty sheep magnet from the fridge and he sticks nicely to the feed”T.

Time to get the hacksaw out again 🙂

Thanks all

don – slight hijack – I posted up on your CDF freehub thread the other day…