Leak ?

[dormermike]

Hi

Got an early 90's Y Plan open vent system with an ancient but dependable ideal Mexico 2 boiler. System works fine except for having to bleed the boiler radiator (don't know what it's called, the one without a TRV on it) every week or two.

I have tried all sorts including a plumber / heating engineer who couldn't find anything wrong besides the vent bend being too low over the header of the F&E tank. So it may be drawing in air.

However I cleaned out the F&E tank a while back (2 months) and left the filler tap closed. The level has not dropped at all but I've been bleeding air out!!

So what could be going on here? The level doesn't drop in the tank but I'm bleeding air out.

Am I right in thinking the feed is blocked and its breathing through the overflow, and whilst the level in the tank is not dropping, the actual level in the system must be dropping because no new water is coming in to fill the void left by air bled out?

Or could this indicate a leak somewhere? Absolutely no sign of one anywhere though.

Thanks
Mike

 

[Burnerman]

It takes a fair bit of bleeding to alter the level in the flow and expansion tank.....on occasion the fill valve lets a little water through anyway.
When you do bleed, are the bubbles and water black?
John

 

[dormermike]

Hi

Yes the water is black

The water level hasn't budged at all yet the radiator can be almost empty (judging by the hot/cold line).

Thx

 

[cross thread]

Could be hydrogen , the test used to be see if it lights !! Dirty systems can produce it

 

[snb]

There can be a few causes for air to accumulate in a rad.
1 rad will always collect more than any other.
Can be system degrading in which case you get hydrogen.
Most common is leaking radiator valves and pump valves( not leaking water but on the negative pressure side allowing air to be drawn in).
Slight kettling within boiler exchanger

 

[Burnerman]

The black solution is called magnetite which is actually deoxygenated rust, which is why its black rather than brown.
As said, it is an excellent hydrogen producer and indicates that the system probably could do with a clean.
John

 

[dormermike]

Thanks all.

I've had 2 litres of x400 swishing around in the system for about 8 weeks so I could do with draining it down and replacing with clean water and x100.

Hydrogen is a good point I'll try and ignite the air that is expelled.

When I had a plumber look at it he painted green stuff over various parts of the pump etc to try and stop air being sucked in. Made no difference.

Changing the height of the expansion tank water level (float adjustment) has made no difference, neither did extending the overflow pipe (temporarily!) to below the water line.

 

[John D v2.0]

made no difference, neither did extending the overflow pipe to below the water line.

that's wrong, if it's pulling air down the expansion pipe it needs to be connected at the same point of the system, otherwise it'll be circulating water through the tank which causes corrosion and a warm tank

 

[dormermike]

that's wrong, if it's pulling air down the expansion pipe it needs to be connected at the same point of the system, otherwise it'll be circulating water through the tank which causes corrosion and a warm tank

Sorry just to clarify I temporarily extended the outlet down below the water line just to see what happened. Made no difference and mod since removed.