Megaflo Air Gap Replenish Problems

[GDEvans]

I have a 20 year old Megaflo CL170. I have lived in the house from new, so I am used to replenishing the air gap.

However, I seem to be experiencing problems retaining the air gap. I get hot water when the boiler is on. But when the boiler is off, the amount of hot water is very limited.

I am aware that unvented systems can only be serviced / modified by a suitably qualified person. I do not intend to carry out any work myself. I just need a little knowledge so I can speak to the plumber with a level of understanding of these systems. I am a civil engineer with experience of large scale industrial pipework, so I have some knowledge!

I followed the instructions and isolated the water supply to the Megaflo. In case this valve was the problem, I also tried turning off the main stopcock to the house. In both cases the results were the same.

When I turned on the lowest hot tap (ground floor tap - cylinder on 2nd floor) the water started to flow. But it did not stop after a few minutes. Half an hour later the water was still flowing slowly but constantly from the hot tap. In the cylinder I can hear the water flowing.

Upon opening the pressure relief valve, I get a lot of gurgling, but no water flowing into the tundish.

Any suggestions on what may be the problem here? Has something failed within the cylinder?

 

[HERTS P&D]

When you turned off the main stopcock, did you open the cold kitchen tap to confirm that the stopcock was shutting off completely?

Andy

 

[GDEvans]

When you turned off the main stopcock, did you open the cold kitchen tap to confirm that the stopcock was shutting off completely?

Andy

Yes. The main stopcock is functioning correctly. When off there is no water from any cold tap (all directly supplied - no cold water tank).

I am confident that the Megaflo supply valve is also functioning correctly and stopping the incoming flow. After running the hot tap, with the valve off, when I open the valve the water gushes noisily into the cylinder.

 

[oldbuffer]

1. As first guess I would suspect the plastic baffle for the air gap has broken / disintegrated. In consequence the cylinder will be over full, which could account for the ground floor hot continuing to run for a good while.
2. If you have a meter, try turning the water off at the meter stopcock, in case the cold supply to your cylinder is not controlled by the stopcock you have used previously.
3. Not sure about MegaFlo's, but some cylinders can be fitted with an external expansion vessel. If your's can you might be able to avoid replacement, at least for a while.

 

[GDEvans]

1. As first guess I would suspect the plastic baffle for the air gap has broken / disintegrated. In consequence the cylinder will be over full, which could account for the ground floor hot continuing to run for a good while.
2. If you have a meter, try turning the water off at the meter stopcock, in case the cold supply to your cylinder is not controlled by the stopcock you have used previously.
3. Not sure about MegaFlo's, but some cylinders can be fitted with an external expansion vessel. If your's can you might be able to avoid replacement, at least for a while.

Thanks for your reply. I have tried turning off both the valve at the Megaflo, and the stopcock for the whole property. Either way the result is the same.

Point 1 was what I was hoping not to hear...