Aga and Boiler heated central heating problem!!!

[Pullerama]

Ok this will test you but I could do with some advice as two plumbers I've talked to about it have offered small comfort!
I have just moved into a house that has an old floor mounted boiler and an Aga side by side in the kitchen, both Gas fired.
The Aga has been on since day one and heats the hot water via a gravity fed heating loop to a storage cylinder in the bathroom (indirect single coil), this works great.
I recently had the boiler serviced and as the weather got a bit chilly a couple of weeks ago I decided to fire this up. It appeared to be working fine for the first week, hot rads all round the house (15 in total, two stories).
Then at the weekend, after I'd shut a few of the rads down during the week to save wastage, I noticed that there was some hot water (rusty in colour) venting from the overflow onto the roof.
I went up into the loft to see one of the two vent pipes pumping hot water into a full expansion tank (right hand). A second expansion tank (left hand) was almost empty with the ball valve open and gushing cold water.
I immediatley shut the central heating down and everything reverted to normal aga heats the hot water and I have no heating to the Rads!
The boiler and the aga heating loops appear to be linked and I discovered that the feed pipe from the initial over flowing tank was blocked, so I've unblocked it.
When I drain some water off the system both expansion tanks drain evenly, but now when I fire the CH up, rather than over flowing from the vent pipe in the right Expansion tank, the left expansion tank water level drops and the right tank fills through the feed pipe and over flows???
I could really do with someone who knows what they are doing here! ww've just had our first child and need to get this working!

Any help advice or diagnistic checks are all welcome?
Pullerama

 

[twgas]

As you have two f&e tanks but, aparrently, only one system I would summise that your cylinder was changed from a 2 coil to a one coil and linked together in an incorrct manner or boiler originally only supplied CH and Aga only HW.
I would be either looking at putting a twin coil back in or splitting the boiler from the HW and have it only doing the CH

 

[Boilerman2]

Sounds like it was installed by the MUPPETS!!
The Aga should be on its own Indirect cirucit, the heating on a second with possibly hot water provided by a second indirect coil in the cylinder Just a thought? have the Open Vent pipes going over the right F&E TAnks? as if these were wrong the one that was pumping over would be filling the wrong tank, which could explain why the 2nd tank ball valve was going flat out? I would do some investigation into the vents to ensure taht they vent over the correct tank

 

[twgas]

have the Open Vent pipes going over the right F&E TAnks? as if these were wrong the one that was pumping over would be filling the wrong tank,

Good call BM2

 

[Boilerman2]

Yeah i'd better sit in a Dark room for an hour and listen to Mozart

 

[twgas]

Yeah i'd better sit in a Dark room for an hour and listen to Mozart

will this do http://www.youtube.com/watch?v=VmjGDBWZZFw

 

[Goldberg]

You need to sketch out for yourself the pipe layout, focusing particularly on the sequence of connection of the two cold feeds and two vents relative to the pump.

 

[oilman]

I could really do with someone who knows what they are doing here! ww've just had our first child and need to get this working!

You could do with some one. What small comfort did the plumbers offer? It's possible the system has worked ok at sometime, now it has a fault that needs fixing, but an internet forum won't do it as we can't see what you've got. An Aga heating water is an expensive luxury. Agas are cookers, and are very inefficient water heaters.

As for being installed by muppets, there is no evidence to support that view. It would be useful to find out what the problem is, but it probably won't be cheap.