Just 42% of energy customers who have switched supplier since they got a smart meter managed to keep their equipment working, exclusive Which? research reveals.
Some 19% of people found that their smart meter stopped working when they switched, and a further 29% said that both their smart meter and in-home display no longer worked. So, in total, 48% of smart meter owners who switched found that their meter stopped working afterwards.
What's more, 11% said that their in-home display (the device showing near real-time energy use and cost) stopped working when they switched, although their smart meter stayed smart.
If your smart meter loses its smart functions, it will stop sending your gas and electricity meter readings to your energy provider automatically. You'll stop getting real-time data on your energy use and, because it's operating in 'dumb' mode, you won't be able to access smart meter tariffs or get insight into your energy use.
Around 943,000 smart meters are operating in dumb mode at the moment, according to the National Audit Office (NAO) which published a report on the smart meter roll-out in November 2018. That's out of a total of 13.65 million smart meters installed across homes and small businesses.
Our research found that just 42% of those who have smart meters and switched energy firm ended up with both a smart meter and an in-home display that still worked.
According to government data, 69% of the smart meters installed by large energy firms were fitted in the past two years. Many people with these meters won't have switched suppliers yet, so the total of smart meters operating in dumb mode is likely to rise.
Some 17% of those with smart meters had switched supplier since having it fitted, our survey revealed.
There are two types of smart meter - first and second generation. Most of the smart meters installed so far are first-generation, and it's these meters that are affected when you switch provider.
You can switch supplier with second-generation meters and keep their functionality. That's because they're connected to a central wireless network that all energy firms can use.
But first-generation meters haven't been enrolled into this network yet, and companies can't necessarily use each other's systems.
If you have a first-generation meter and don't plan to switch energy supplier, you won't be affected. However, switching energy supplier is crucial if you're keen to get the best deal for you.
All smart meters should have their smart functions restored by the end of the roll-out (the end of 2020), the government says.
First-generation meters will start to be enrolled into the wireless network later this year, so that all suppliers will be able to read them.
But this might not work for some meters, and there are no plans to enrol meters made by certain brands. Most of the meters that aren't included in the enrolment plans are Secure meters.
On 4 March 2019, the Department for Business, Energy & Industrial Strategy (BEIS) launched a consultation to seek views on its proposal for the Data Communications Company (DCC), which manages the wireless network, to enrol the remaining first-generation Secure meters. Some of the factors include whether these devices offer an acceptable level of security and whether the enrolment is technically possible. The consultation ends on 2 April.
In the meantime, some companies have agreements in place, or compatible software, meaning they can use rivals' smart meters. Find out more in our guide to . Before you switch, check with your chosen firm that they will be able to read your smart meter.
Ultimately, any meters that can't be connected to the wireless network will be replaced with second-generation meters - also by the end of 2020. In the end, smart meters should enable you to switch providers more quickly.
We surveyed 2,910 members of the GB general public who have smart meters. This was part the broader energy companies online survey of 8,000 members of the public in September 2018.