Tenants Derek Cookson, 77, along with wife Joyce, 79, of Danes Close, were exposed to deadly fumes after repeated calls to Gedling Homes about the boiler being broken.
Mrs Cookson was rushed to hospital and Mr Cookson was left on the verge of collapse.
Now Gedling Homes has brought in an independent surveyor who is investigating the cause of the leak, alongside the Health & Safety Executive.
The charity National CO-Gas Safety had yesterday called for an independent investigation.
Stephanie Trotter president and director of CO-Gas Safety, said they have been monitoring the couple's situation since they read their story in the Evening Post.
The charity has campaigned for increased awareness about the threat of carbon monoxide poisoning since 1995.
Only CORGI engineers are allowed to work on gas appliances by law. No similar rules exist for those who have solid fuel burners, like the one in the Cooksons' home.
Mrs Trotter said: "We have always lobbied that solid fuel engineers should be registered by law."
On November 29, records left by an engineer who visited the Cooksons stated he was not trained to deal with solid fuel burners. Their daughter, Carole had already explained what type of boiler her parents had.
Jim Lambeth, general manager of advisory service, The Solid Fuel Association, said: "From the pictures I have seen the boiler is clearly in a poor state and vital maintenance has not been carried out.
"In any rented property, it's the responsibility of the landlord to maintain the boiler to keep it in working order and it's the tenant's responsibility to carry out routine maintenance.
"HETAS are a group who hold a list of approved solid fuel engineers but effectively anyone can be employed to service a solid fuel boiler. That's the problem, a council can employ anyone legally to do the job."
Lynne Clayton, managing director at Gedling Homes, said: "We are working hard to get Mr and Mrs Cookson back to their home. Specialist contractors are working today to ensure they can return safely which will be before the weekend. Temporary heating and hot water are in place. With Mr Cookson's agreement, a gas meter is being installed, and we will put in a new central heating system."
Mr Cookson, an ex-miner, used anthracite to fuel his boiler. A hard, compact variety of mineral coal, it can leave a residue in the flue of a boiler and if this is not properly maintained, it can lead to a blockage and fume leaks containing carbon monoxide