New Radiator - how much bleeding?

[wedge69]

Hi, have a sealed heating system that we had drained and refilled back in the summer following the addition of a larger radiator and the replacement of some valves. We have sixteen radiators in total.

Had the heating on since the start of November, and every couple of weeks we get a gurgling and I have to bled the towel rail.

I can't find any obvious leaks, so is this just a matter of trapped air finally finding its way through? Basically, following a drain and refill, how many times should the system need bleeding.

Thanks

 

[Harry Bloomfield]

The bleeding routine can take many weeks, to get all the air out. As time goes on, the amount of air coming out, during each session, should become less.

If the problem doesn't reduce, I would be questioning whether inhibitor in the system is adequate.

 

[wedge69]

Many thanks. That puts my mind at rest.

When the work was done a full bottle of inhibitor was added. Will trust the plumber that this was enough.

 

[oldbuffer]

1. If its a combi boiler, ignore the following.
2. Assuming the hot water is heated in a hot water cylinder, it is possible for air to be trapped in the coil within the cylinder.
3. Hot water from the boiler passes through this coil and heats the water in the cylinder without ever touching it. (Indirect heat).
4. There will be two connections to this coil, one near the base of the cylinder and the other about 1/3rd the way up. They are normally vertically aligned with each other.
5. The upper connector should have the boiler flow pipe going into it, and the lower connector is for the return.
6. Good practice is for there to be an air vent, usually on a stub of 15 mm pipe, coming from the upper connector or from the pipe going into it.
7. This may be a manual air bleed valve (e.g. Screwfix 52451) or an automatic air vent (e.g. Screwfix 34359).
8. If a manual vent, slacken, but do not remove the knurled screw at the top to vent air out. When water comes out, re-tighten.
9. If an automatic vent, slacken, but do not remove, the plastic or brass cap (like a tyre valve cap) on top to vent air out. When water comes out, re-tighten. In theory the caps can be left loose, but in practice these valves usually leak.
10. Do the above after running the system (CH and HW) for 10 minutes or so, then turning the system off and waiting for a further 10 minutes for air to settle.

 

[wedge69]

It is a combi boiler but hopefully your advice can help others!