NIGHTMARE GRAVITY SYSTEM!

[Jonathanjc]

All,

Need some ideas pleaeses and thanks.

Customer had drained system and had awful air locks, went round boiled out and got working... GREAT!

2 weeks later after some bumping and banging, no hot water. Went round and flow red hot, nothing on the return.

Boiled again... Got hot water... Worked perfectly for around 2 weeks and then same pattern.

The header tank is in a super awkward position (in a small cupboard with the roof straight above behind the larger dhw tank). I noticed that the vent pipe was in the water, so I cut and lifted. I have also popped a thumb vent on the return. Boiled again, got running and this time after 11 days and some more noise there is once again no hot water.

The gravity valve is somewhat (somewhat being a debatable word) accessible, I'm going to swap this out... But really bloody scratching my head!

THOUGHTS WELCOME!

 

[Chuck]

THOUGHTS WELCOME!

I find it difficult to understand the history and layout from your description.

Why did the customer drain it in the first place? By 'boiled it' I assume you mean you deliberately increased the flow-temperature from the boiler to encourage circulation.

If this is an old vented gravity circulation system then there's a good chance the pipes are partially blocked with sludge. Draining may have moved some of this downwards and it's built up somewhere critical.

If the gravity valve is okay, try cleaning and flushing the the circuit with mains water or a power flusher. Then fill upwards from the drain point rather than downwards from the F&E tank.

I'd seriously consider upgrading it by converting to a pumped system. If it's old you can spend quite a while trying to flush and still not get it clean enough for gravity circulation to work reliably.

 

[Last Plumber]

I would tend to agree with Chuck.
It struck me that if the vent was in the water, the pipes may have sunk/dropped over the years.
Did you try to lift them? They do need to rise all the way from the boiler to the coil.
Obviously not seen it and the vent will probably come off the top of the coil so if it rises up off that, then the chances of it having moved are small but if it travels any distance sideways before it rises, then it is a possibility.
Hope that makes sense?

 

[Jonathanjc]

Right...

I've calmed down now!!!

The boiler is very old and I'm thinking it's creating air anytime it boils slightly.

The customer does not want to go for valves as this would mean ripping out kitchen cupboards so I've come up with the following....

Stick a pump on the gravity hw pipe and a non return valve on the gravity pipe and ch pipe. Wireless cyl stat and timer for he and heating. The pump will act as a valve. I will also need to put the feed and vent on the return (vent currently on flow).


Thoughts please experts.....!

 

[Jonathanjc]

I would tend to agree with Chuck.
It struck me that if the vent was in the water, the pipes may have sunk/dropped over the years.
Did you try to lift them? They do need to rise all the way from the boiler to the coil.
Obviously not seen it and the vent will probably come off the top of the coil so if it rises up off that, then the chances of it having moved are small but if it travels any distance sideways before it rises, then it is a possibility.
Hope that makes sense?

I did lift the vent

 

[Last Plumber]

Vent needs to be off the flow to the boiler for safety and a pump on the gravity circs will cause it to pump over.