Here's something that surprises a lot of homeowners. Two neighbours can have the exact same heat pump fitted a week apart and end up with completely different results. One gets a warm house and bills that finally behave themselves. The other gets cold bedrooms, a fan humming away all evening and a bill that's somehow gone up.
It's rarely the heat pump's fault. What changed was the survey, the design and the person holding the drill. That's where experience earns its keep. So this guide is about choosing an energy efficiency company you can actually trust. We'll look at the accreditations worth checking, the warning signs worth walking away from, and what you can do if a job goes wrong anyway.
Short Answer: With home energy upgrades, how it's fitted matters every bit as much as what's fitted. Make sure the installer has the right accreditation for your particular job, because it differs from one job to the next. Don't accept a quote from anyone who hasn't been round to look. Ask to see houses like yours they've already done. And if someone's pushing you to sign today, let them push someone else.
Key Facts at a Glance
- In October 2025 the National Audit Office reported that roughly 98% of homes fitted with external wall insulation under the ECO4 and GBIS schemes had major faults needing repair. That's an estimated 22,000 to 23,000 households.
- Internal wall insulation under the same schemes didn't do a lot better, with major issues in about 29% of homes.
- No MCS certified installer, no £7,500 Boiler Upgrade Scheme grant. The same goes for Smart Export Guarantee payments on solar.
- It's the law: anyone working on a gas boiler in Great Britain must be on the Gas Safe Register.
- Signed a contract at your kitchen table rather than at the installer's office? You'll usually get 14 days to change your mind.
Why Does Experience Matter for Energy Efficiency Work?
Because the kit is only half the story. Insulation, heat pumps and solar panels all live or die by small design and fitting decisions, and those decisions are different for every house. Get them wrong and performance quietly drops. Get them badly wrong and you're looking at damp, mould or water coming through the ceiling. An experienced installer has seen most of those mistakes before, usually in someone else's house, and knows how to steer clear of them.
The Lesson From the ECO4 Insulation Failures
If you want proof, have a look at what happened with the government's ECO4 and Great British Insulation schemes. In October 2025 the National Audit Office found that around 98% of homes given external wall insulation under them had major problems. Not cosmetic stuff, either. Many of the faults lead to damp and mould, and a handful were genuinely dangerous, like live cables left exposed or boiler ventilation blocked off.
The NAO blamed weak oversight and firms cutting corners. So what should a homeowner take from it? Mainly that a logo on the side of a van guarantees nothing. You want a firm that designs the job properly, sweats the small details and is still answering the phone a year later.
No Two Houses Are the Same
Take a 1900s terrace in Wolverhampton and a 1990s semi in Solihull. Almost nothing about them matches, from the walls and the roof to the heating they've got now and whether there's anywhere to put a cylinder. Even which way the house faces makes a difference. A good team will happily tell you when something isn't right for your home. A bad one will sell you whatever's on the van. (We go into which upgrades suit your type of home in a separate guide.)
What Can Go Wrong When Upgrades Are Fitted Badly?
More than you'd think, and a fair bit of it doesn't show up until the first proper winter. Poor workmanship hides in the fiddly bits. The edge of the insulation round a window. A radiator that's one size too small. A fixing driven through a roof tile at the wrong angle. Here's where it tends to go wrong, and what a good installer does about it.
| Upgrade | What poor workmanship can cause | What a good installer does instead |
|---|---|---|
| External wall insulation | Gaps around windows and edges, water getting behind the render, damp and mould inside | Plans every edge and junction, extends sills and rooflines where needed, checks ventilation |
| Cavity wall insulation | Damp where walls face driving rain or the cavity is full of rubble | Checks the wall's condition and exposure first, and says no if it isn't suitable |
| Loft insulation | Blocked ventilation at the eaves, condensation in the roof space | Keeps airflow clear at the eaves and raises any boarding instead of squashing the insulation |
| Air source heat pump | Wrongly sized unit, radiators too small, cold rooms and high bills | Room-by-room heat loss calculation, radiator sizing, proper commissioning and handover |
| Solar PV | Cracked tiles, leaks, badly routed cables, panels sitting in shade | Roof survey first, proper fixings, certified electrical work, shading assessment |
| Gas boiler | Unsafe work, poor efficiency, controls never set up | Gas Safe engineer, correct commissioning, controls explained to you |
Why Design Matters Most With Heat Pumps
This is where design really earns its money. A gas boiler can cover for a draughty house by blasting out heat. A heat pump can't. It works at lower temperatures for longer, so if nobody did a proper heat loss calculation, or the radiators were left as they were, some rooms just never get there. Meanwhile the system runs flat out and the bills creep up.
Do the design properly and the very same heat pump can be cheap to run and lovely to live with. It's the reason an MCS certified installer has to follow MCS design standards. Ask to see the heat loss figures behind any quote. If they can't show you, that's telling.
Which Accreditations Should an Energy Efficiency Installer Have?
Depends entirely on the job. There's no single badge that covers the lot, so you need to match the accreditation to the work. An accredited installer doing heat pumps needs completely different paperwork from someone laying loft insulation.
| Type of work | What to look for | Why it matters |
|---|---|---|
| Heat pumps, solar PV and batteries | MCS certification | Needed for the Boiler Upgrade Scheme grant and Smart Export Guarantee payments |
| Gas boilers and any gas work | Gas Safe Register | A legal requirement for anyone working on gas |
| Electrical work, including solar | A competent person scheme such as NICEIC or NAPIT | Lets the work be self-certified under building regulations |
| Insulation and other retrofit work | TrustMark registration and PAS 2030 / PAS 2035 | Government-endorsed quality standards, required for funded schemes |
| Wall insulation | An independent insurance-backed guarantee, for example from CIGA (cavity) or SWIGA (solid wall) | Protects you if the installer stops trading |
| Extensions and renovation | Building control sign-off for notifiable work | Confirms the work meets building regulations |
What Changed With MCS in 2026?
MCS has been moving installers over to a redeveloped scheme during 2026, and a couple of things have changed. Installers on the new version no longer have to belong to a consumer code like RECC or HIES. Complaints about MCS installations now go straight to MCS, rather than through the codes.
Check the Certificates Yourself
Two minutes, honestly. MCS, Gas Safe and TrustMark each have an online search where you can look a business up by name or registration number. Gas Safe engineers carry an ID card too, and nobody decent will mind you asking to see it. A properly accredited installer will rattle off their numbers without a second thought. If someone goes vague on you, you've got your answer.
How Can You Tell If an Installer Really Has Experience?
Ignore the claims and look for proof. Anybody can put "years of experience" on a website. What you're after is evidence they've done jobs like yours, and done them well.
What a Good Survey Visit Looks Like
The first visit tells you a lot. A proper surveyor won't be in and out in ten minutes. They'll measure up rooms and windows, stick their head in the loft and look at the walls inside and out. Every radiator gets noted, and if there's electrical work involved they'll want a look at the meter and fuse board. For solar, expect them to spend a while staring at your roof and asking where the sun is in the afternoon.
They should be asking you questions all the way round. If most of the visit goes on finance options, make a note of that.
Signs You're Dealing With a Good Installer
- They come round before quoting and actually take their time over it.
- They want to know how you live. Who's in during the day? How many showers a morning? Which room does everyone avoid in January?
- They'll tell you what won't work, not just what will.
- You get the quote in writing, broken down line by line, with the design behind it, like a heat loss calculation or system size.
- They can point you to similar houses nearby, and past customers are happy to have a chat.
- They're straight with you about warranties, aftercare and who you ring when something's not right.
Red Flags Worth Walking Away From
- "Sign today and we'll knock 20% off." Any deal that disappears if you sleep on it.
- A heat pump or solar quote over the phone, with nobody having set foot in the house.
- A chunky deposit and no clear answer on how it's protected.
- Fuzzy answers about accreditation, or paperwork with no registration numbers on it.
- Guaranteed savings. Real savings hang on your house, your tariff and energy prices, and those prices won't sit still. (Here's why your energy bills keep rising.)
- Insulation quotes that don't mention ventilation once.
- Out-of-the-blue calls or doorstep visits saying you qualify for free upgrades. Some schemes are real, but check for yourself before agreeing to anything.
Who Will Actually Do the Work?
Funny how rarely people ask this one. Some companies sell the job and then hand it to subcontractors you've never met. That isn't automatically a bad thing, but you should know about it up front. Ask who'll be on site, whether they're employed by the company and who's running things day to day. If you're paying an MCS certified installer, check they stay responsible for the whole installation, even if bits of it get subcontracted.
And bigger doesn't always mean better. A national brand might have a glossy website and a call centre. A local firm with its own trades knows the houses round here and will still be about when you need them. In the end it comes down to who turns up, how good they are and whether the company stands behind them.
What Should a Proper Survey and Quote Include?
A survey that looks at the whole house, and a quote that spells out exactly what you're paying for. If two quotes are miles apart on price, odds are one of them has left something out.
| What to look for | Why it matters |
|---|---|
| Room-by-room heat loss calculation | Makes sure a heat pump or new radiators are sized for your house |
| Ventilation check | Insulation without enough ventilation can cause condensation and mould |
| Roof and structure check | Solar panels need a sound roof that can take the fixings and the weight |
| Make, model and size of every product | Lets you compare quotes like for like |
| Who handles building regulations and any planning | Stops gaps that nobody takes responsibility for |
| Payment schedule and deposit protection | Protects your money if the firm runs into trouble |
| Warranties and guarantees in writing | Shows what's covered, for how long and by whom |
| Handover and aftercare | You should know how to use the system and who to call |
Curious what that looks like in practice? Our guide to how our survey and installation process works walks through it at Greentek.
Why Does Building Experience Matter for Energy Upgrades?
Because most home energy upgrades are building jobs at heart. Proper external wall insulation and rendering means scaffolding, shifting drainpipes and satellite dishes, and extending window sills (sometimes the roofline too) so rainwater runs off where it should
A heat pump isn't just a box bolted to the outside wall either. A decent air source heat pump installation can involve new pipework, bigger radiators and finding a home for a hot water cylinder. And a solar PV installation is never better than the roof it's sitting on.
When those knock-on jobs fall between different trades, that's exactly where things get missed. With a team that's got building experience, it all sits with one firm from the first visit to the last bolt. You're not stuck chasing three contractors who each blame the other two.
What Are Your Rights if Something Goes Wrong?
The Consumer Rights Act 2015 says a trader must do the work with reasonable care and skill. If they haven't, you can ask them to put it right. If that doesn't happen, you may be able to claim a price reduction.
There's a cooling-off period too. Sign at home, or anywhere that isn't the trader's premises, and you normally have 14 days to cancel. One catch. If you asked them to start within those 14 days and then cancel, you might have to pay for whatever's been done.
If a complaint gets stuck, push it up the chain. For MCS work that's MCS itself, or the installer's consumer code if they're in one. Trust Mark can step in for its registered firms. For anything else, Citizens Advice is a good free first stop. (This is general information, not legal advice, so get proper help if things turn serious.)
Whatever happens, keep a paper trail. Photos before, during and after. Every email and text. The dates problems started. You'll be glad of it if you ever need to complain.
What Should You Do Before You Sign? A Step-by-Step Checklist
- Get at least three quotes. The Energy Saving Trust recommends it, and it's the fastest way to spot the one that's missing something.
- Check the accreditations yourself. MCS, Gas Safe, TrustMark, whichever fit the job. Use the official registers, not the logos on the quote.
- Ask to see similar work. Photos, houses you can drive past, customers you can ring.
- Make sure the survey covered everything. Heat loss, ventilation, roof or structure, whatever's relevant to your job.
- Compare like with like. Same system size, same products, same warranties. The cheapest quote and the cheapest job aren't always the same thing.
- Know how your money's protected. Deposit, stage payments and any insurance-backed guarantee.
- Read the contract properly. Start date, what's included and your right to cancel.
- Agree what you'll get at handover. Certificates, guarantees, manuals, and someone actually showing you how to use the thing.
Getting Expert Help in the West Midlands and Wales
Picking an energy efficiency company really comes down to deciding who you trust with your house. The right accreditation matters. So does a survey that isn't rushed, and a team that can show you work like yours. Tick those off and most of the risk disappears.
Greentek Energy Ltd is one accredited team for building work and energy upgrades, from insulation and rendering to heat pumps, solar PV, battery storage and full renovations. We cover the West Midlands and Wales, including Coventry, Birmingham, Solihull, Wolverhampton, Dudley, Cardiff and Swansea. Want a straight answer about what your home actually needs? Give us a ring on 0333 533 4567 or book a free consultation.
