I used Centrona for 5+ years to service the boiler on my rental property and took out their insurance policy for breakdown/replacement. After 5 years, boiler completely broke down for first time and no heating/hot water for tenants.
Although Centrona visited next day, they didn't repair it. Unlike most tradesmen, Centrona don't advise the landlord of the issue/next steps - you have to call their office and chase it usually 3-4 times over a few days and go through Chinese whispers with the office rather than speaking to the engineer.
I was finally advised it would need a power flush for £900 (which isn't covered by the insurance I had taken with them) despite Centrona's own website quoting £400 for a power flush of this size and the system being fully flushed 5 years earlier and radiators previously heating well. When I raised this, Centrona didn't have an answer and I was basically told the engineer is qualified so that's the situation and that's his quote.
I paid to have a second engineer from a different company look at the boiler. Communication was far better with photos, videos and an in-depth call whilst at the appointment. He immediately shut down the boiler due to gas safety and showed the parts that had failed. The whole boiler unit needed replacing - the power flush Centrona quoted for was irrelevant to the issue and the water was clean and clear.
Centrona had serviced and cleared the boiler two months prior and never mentioned any of the issues building up that caused the failure, or even when they visited on the breakdown. The second company could not believe I was quoted for a power flush to fix the issue and doubted previous boiler services had been done properly.
After being a loyal customer to Centrona for years, their service completely failed when I needed it.