the end of the day as you say you have joined the upstairs return into the downstairs return then run one return back to the boiler, theres no reason for you to get reverse circulation unless you had two rad returns.
Just to say thank you for all who posted, I finally fitted the system and tested and for the record there was no reverse flowit worked really well.
Once again thx
Paul
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local