Radiator water fizzy?

[m0t]

I bled one of the two radiators in the bedroom earlier and quite a bit of air came out and then the water that came out after that was fizzy, not hugely but enough to keep bubbling for a while in the cup I used (plus it was obviously frothy as it came out of the rad).

I suspected there might have been air in the system because I drained it completely earlier in the year to relocate a radiator so had lots of the pipe apart under the floor downstairs.

I've not ever had fizzy water out of a rad before, should I be worried about that? The rad next to it was fine.

System is a gas combi with 7 rads on it.

 

[muggles]

Could be hydrogen rather than air, in which case you have a serious corrosion problem that needs attending to ASAP

 

[m0t]

What would cause that?

For info the boiler is 4 years old, the rads are all between 0-4 years old (as is the pipework), there's a magnaclean fitted which never looks particularly dirty and the water I flushed out last time was completely clear.

We live in a hard water area and I used a sentinel inhibitor when refilling the system.

 

[Nige F]

Could be a micro leak on a negative pressure area of pipework, drawing air in.