Viessmann trained · Gas Safe registered · London
Boiler installation, replacement, repair.
Whether you are replacing a failing boiler or building a full new system, we install combi, system and regular boilers from Viessmann, Worcester, Vaillant and Ideal. No commission-driven upsells — just the right kit for your home.
What we fit
Gas, electric, and hybrid — specified for your home.
A boiler is a fifteen-year decision. Getting the size right — not too big, not too small — matters more than the brand on the box. An oversized boiler cycles on and off, wastes gas and wears out faster. An undersized one struggles in winter.
We install combi boilers for smaller flats and houses where mains pressure is good and space is tight. System boilers with an unvented cylinder where you have multiple bathrooms and want strong simultaneous flow. Regular (heat-only) boilers where you have an existing tank-and-cylinder setup that still makes sense to keep.
We're Viessmann-trained as our primary manufacturer, and we also fit Worcester Bosch, Vaillant and Ideal where the application fits. We'll recommend what's right — not what earns us the biggest commission.
Why Thermalwerk for boilers
Proper heat-loss sizing. Transparent pricing. Work you'll want to show your friends.
Sized properly.
Full heat-loss calculation, not a guess based on bedroom count. You get a boiler that runs efficiently, not one that short-cycles itself to an early grave.
Power-flushed as standard.
System cleaned chemically before and after the swap. Magnetic filter fitted. Inhibitor dosed. You get warranty coverage that actually holds up if something goes wrong later.
Fixed price quote.
Everything included. No "oh, we hit a snag" surprise invoices on completion day. Survey first, price second, install third.
Extended warranties.
Up to 12 years manufacturer warranty on Viessmann and Worcester installs when we complete annual servicing. Registered on your behalf, papers in your inbox within the week.
Clean finish.
Pipe runs boxed properly, condensate drain routed neatly, flue terminal sited where you don't have to look at it. The stuff you don't notice is where we do our best work.
Smart controls done right.
Tado, Hive, Honeywell Evohome, Nest — fitted and commissioned properly with weather compensation where the boiler supports it. Actual savings, not just a nicer app.
Common questions
The boiler questions homeowners ask us most.
How much does a new boiler cost in London?
A straight combi swap on an existing system typically sits between £2,400 and £3,600 fitted. A full system replacement with new cylinder and pipework changes runs £4,500 to £7,500. We quote properly after the survey — no ballpark figures that move on install day.
How long will it take to install?
A like-for-like combi swap is usually a one-day job. A full boiler-plus-cylinder replacement with pipework changes is two to three days. We'll give you a committed date before we start — not a "we'll let you know" shrug.
Should I get a heat pump instead?
Possibly. It depends on your property, your emitter sizing, your outdoor space, and your appetite for up-front investment. We install both, so we'll give you an honest comparison — not a pitch for whichever earns us more. If a boiler is the right answer for your home right now, we'll tell you that.
What brands do you recommend?
Viessmann is our first choice for build quality, quiet operation and long warranties. Worcester Bosch and Vaillant are excellent alternatives. Ideal for budget-sensitive jobs where the longer warranty is the main driver. We don't fit anything we wouldn't put in our own homes.
Can you fix a boiler that's broken?
Yes. We run a proper repair service — same-day where we can, next working day otherwise. Diagnosis fee is transparent up front, and repair parts are quoted before we fit. If it's beyond economic repair we'll tell you straight.
Customer stories
What homeowners tell us after the install is finished.
Placeholder reviews shown while we build a verified Google and Checkatrade profile.
We had three quotes for a new Viessmann boiler. Thermalwerk was not the cheapest, but they were the only ones who actually explained the sizing.
David K.
Islington · Boiler replacement
Replaced our old combi with a heat pump. Quiet, much cheaper to run, and the team left the plant room tidier than they found it.
Rachel M.
Dulwich · Heat pump
Two Daikin units fitted across an open-plan living space. Clean cable runs, properly commissioned, works brilliantly. Glad we waited for them.
Priya S.
Kensington · Air conditioning
Talk to us
Ready to replace or repair a boiler?
Tell us what you've got, what's gone wrong or what you're planning, and we'll come out for a proper look. Quotes are free and fixed — not ballparks that move.