Here’s a little thought, raised by a customer of ours, I hope someone has a better answer than the Insurance Companies.
I’ve just been called out to investigate the cause of a fire, from a newly installed wood burning stove. The cause was very simple to deduce - the fire started in the chimney, burning though a timber support that was incorrectly placed (too close to the flue pipe contravening Building Regulations). This then set fire to plaster board placed incorrectly to the stove (again Building Regulations) and finally the register plate collapsed, bringing combustible soot onto the top of the hot stove.
The stove was installed by a builder (a friend of the family). Unregistered with HETAS (the regulator body governing solid fuel installations, just as CORGI governs gas), and obviously incapable of installing such an appliance to governing regulatory standards.
The client is unwilling to name the builder as he had been "doing them a favour".
Whilst I was there the client had a phone call, from their insurers to discuss the fire and the damages. As I was writing my notes, trying not to listen to the client becoming more and more irate ... ...
The the conversation went something like this:
Client - "You’re HETAS registered aren’t you?"
Me - "Of course"
Client - (Demanding) "good, when you’ve checked the installation and reinstalled the stove, do I get a certificate?"
Me - "Of course, every one of our installations, or in fact REINSTALLATIONS to put right incorrect works, will be certified"
Client - "Good, you’ll backdate the certificate for me then, to, say a week or so BEFORE the fire!"
Me - "Sorry, but no."
The next is exactly what happened, no word of a lie, the client walked up to me, nose to nose, and shouted …..”You f****** moron, without a certificate I don’t have any insurance, what are you going to do about it????”
And me, the moron? My company is registered with HETAS, we follow Building Regulations. I personally know how to correctly install a stove - this is, after all, why I'm in in business.
At this stage you can imagine what advice I gave the Client.
Likewise image - what would happen if you unfortunately had a fire in your house with no accreditation for the stove or fire that you, a friend or any untrained and uncertified person has installed.
Be careful - it seems that No HETAS certificate, could possibly mean No INSURANCE.
Please check with your insurers before commencing any work yourself or with untrained "installers"
You engineer should carry a gas safe card which looks like this: 
