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The worst DIY disasters revealed by Which? Trusted Traders

From costly plumbing mishaps to unsafe gas and electrical work

The worst DIY disasters revealed by Which? Trusted Traders

Doing your own home improvements and repair work can help you to save money – but only if it’s done right. When we surveyed Which? Trusted traders*, 78% of them said that they had been called in to rectify a botched DIY job.

From DIYers attempting to fit or fix their own boilers to overambitious homeowners installing a bathroom with leaky pipes, our traders have seen some horror stories.

The most common cries for help related to plumbing, followed by general maintenance and decorating tasks. While you should always leave gas and electric work to the qualified professionals, some traders we surveyed had encountered and fixed dangerous DIY attempts to fit boilers and hobs, or wire in new electrics. Scroll down for details of the worst DIY disasters our traders have seen.

‘Everyone thinks it’s cheaper to do the work themselves, rather than employ a skilled craftsman,’ said one trader, ‘but it’s a false economy of time and resources to think that way.’

If your home needs repairs, visit Which? Trusted Traders to find a reputable trader who has been through our rigorous checks. 

Worst DIY disasters

Our video highlights five of the most shocking DIY catastrophes our traders have rectified, from plumbing to gas work to electrics:

Read on for more disastrous home improvement stories, as well as advice on what you should – and certainly shouldn’t – do yourself.

Heating and gas

‘I was called out to fix an oil boiler after a guy had tried to install it himself. Every wire had been disconnected in an attempt to make it work.’

‘I have been called out so many times to faulty heating systems, where the customer has tried to fix it themselves. It always ends up costing them more.’

‘We often see gas pipework with the incorrect fittings, and electric showers with no earthing. Both are potentially very dangerous.’

Any work related to gas should be carried out by a Gas Safe-registered engineer. This includes installing, repairing or servicing a gas boiler, and installing or repairing a gas fire, gas cooker or hob.

Man with hand and wrist in bandage after disastrous DIY job

Not all gas engineers are qualified to do all types of gas work. Every Gas Safe-registered engineer should carry a Gas Safe ID card, featuring the Gas Safe triangle.

The engineer’s qualifications will be listed on the back of the card – always check what type of work your gas engineer is qualified to undertake before they begin. Visit our guide to Gas Safe registered engineers to find out more.

Remember that every home should have a functioning carbon monoxide alarm to warn you of potential CO poisoning from gas appliances. In October, Which? is giving away 1,000 CO alarms for free, through Which? Trusted Traders.


‘The worst DIY I saw was a 1.5mm lighting cable that had been used for a ring circuit in a house, when it should have been 2.5mm. A cable like this on a 32Amp circuit breaker is likely to fail or melt under a high load or fault condition before the circuit breaker trips out, putting the whole house in danger.’

‘I do electrical inspections on a daily basis and regularly see really bad wiring jobs attempted by homeowners. Not enough is being done to regulate this.’

Updating, replacing or installing electrics are jobs best left to a professional. Done incorrectly, they could cause a fire, or, in the worst case scenarios, injury or death.

Some electrical jobs need to comply with part-P regulations and be signed off by local authority building control. To avoid having to contact the local authority yourself, hire a trader who is part of a ‘competent person’s scheme’, as they will be able to sign the work off themselves.

Visit our guide to hiring an electrician to ensure you know what to look out for and find a trusted electrician in your area using Which? Trusted Traders.


‘We once went to a job where a customer had tried to change a kitchen sink but, after a number of trips to DIY shops and water leaking everywhere, he gave up and called us in.’

‘I found that someone had incorrectly installed a soil pipe, so their bathroom smelled horrible. We had to dig it back up and start again.’

‘Many people try and fit their own bathroom suite and then wonder why the water isn’t draining away. It’s usually down to poorly installed pipework or no fall/drop on the waste water pipe.’

‘Plumbing might seem easy on the surface. But, without the right tools, the end result can look messy or, worse, leak and damage the house.’

There are some plumbing jobs that DIYers can do themselves, such as bleeding radiators, checking or topping up the pressure in your boiler and testing a stopcock.

But if a plumbing job goes awry, you risk flooding your house, which could lead to ruined possessions, problems with damp and even fallen-in ceilings.

Visit our plumbing section to see all our advice on troubleshooting common plumbing problems and find a reputable plumber in your area if you need one.

Decorating, building and joinery

Man fixing ceiling having falled down

‘We were called to a job where the customer had taken out a wall, but the ceiling hadn’t been checked – it needed steel to support it. We arranged for a structural engineer to calculate what was needed and installed it ASAP’

‘People sometimes try and build conservatories or extensions themselves by joining up bits and pieces they have inherited or by buying something from a supplier and trying to fit it themselves.’

‘It’s very common to see people with roof leaks attempt to cover the hole or crack themselves with a small amount of membrane that they then weight down. This may delay leaks, but never solves the problem.’

‘We see a lot of tiling jobs and wooden floor laying go wrong. The cost to repair/replace it is usually so big that they will never try it themselves again.’

Bigger, structural jobs have a higher risk attached to them – poorly executed DIY could weaken the property or violate building regulations. Before attempting any major work yourself, you should seek advice from a qualified professional and check the rules around building control.

Our advice guides to home maintenance will give you more information on day-to-day jobs and help you decide which are best left to the professionals.

You can also use Which? Trusted Traders to find a builder, roofer, carpenter or painter and decorator in your area.

*Survey of 213 Which? Trusted Traders in May 2018.


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