Has your old, temperamental system boiler finally kicked the bucket? Need a direct replacement?

This problem is actually a lot more common than it might seem, as over the years many customers have called me up looking for the easiest fix for their large, Edinburgh home.

They basically don’t want to deal with any of the upheaval that comes from switching to a combi boiler – and I don’t blame them. Boiler installations aren’t exactly fun, and a quick in-and-out fix is definitely the most attractive option.

This is one of the reasons I tend to recommend is the Vaillant EcoTEC Plus 600 range, as they can allow for a relatively stress-free installation.

Want to know more? Read on for my in-depth review of the Vaillant EcoTEC Plus 637 system boiler:


In my opinion, the Vaillant EcoTEC Plus 637 a fantastic boiler that fits nicely between a 35kW and the 40kW. I’ve used it in the past on occasions where a 35kW or 40kW from other manufacturers has been too large or too small an output.

Getting the output ‘just right’ is sort of like Goldilocks and the Three Bears – only it’s a bit more scientific than that. An engineer should be able to measure your home and check just the right output you need, and getting it perfect is important if you don’t want to be too chilly in winter or paying too much on your heating bills.

This boiler can also be added to your existing cylinder and controls, making it an ideal choice for homeowners looking to make a fairly clean switch from a regular boiler to a system boiler.

The 637 model also has built-in computer wizard which easily guides you through setting up gas pressure and outputs. This allows you to check the range rate for the heating and hot water circuit.

This is also a high efficiency condensing system boiler, so you could notice a difference (for the better!) in your heating bills.

Output and flow rate

This 37kW boiler is designed for a large home, but it can also be suitable for stone built properties with high ceilings and 13 -16 radiators. It will quite happily heat a large 200-litre water tank.

The Vaillant EcoTEC Plus 637 is an ideal choice for someone who does not want a combi boiler system installed, and is looking for a direct replacement system boiler or from a regular boiler to system boiler to heat the radiators and hot water tank in their large property.

This boiler is not suitable for smaller homes (2-3 bedrooms) as it would be oversized and more costly than needed.

Size and special features

The EcoTEC 637 is too big to fit in a kitchen cupboard, but this boiler does pack quite a bunch compared to its relatively small size. Usually my clients prefer to fit these in a cupboard where the boiler and hot water tank can be stored together.

Being an A-rated boiler, the 637 also has a new high efficiency automatic two-speed pump, which will reduce your energy consumption and allows for low stand-by losses – meaning lower energy bills!


Now, this is where there’s a wee bit of bad news. The Vaillant EcoTEC Plus 637 used to come complete with a fantastic no quibble 10-year guarantee. It was a good rival to Worcester Bosch, in fact. However, Vaillant have since stopped offering their extended guarantees (unless you want to pay for them), and this is a huge bummer.

So, now you can expect a 7-year guarantee with the Vaillant EcoTEC Plus. Or, you can pay a little extra for longer (it’s all explained in the link above). So, what’s happened to Vaillant? I suspect it could be the amount of call-outs they were having to do on older boilers. However, this has really affected their market share, which has dropped dramatically.

Similar to Worcester Bosch, Vaillant also has its own dedicated engineers to attend call-outs if you ever need them – so you can be sure your boiler is in good hands if anything did happen to go wrong.

I’m still happy enough to recommend Vaillant guarantees to my customers, as they have no hidden small print or unexpected credit card charges for call-outs, unlike other similar boiler manufacturers. But I’d still put the likes of Ideal or Worcester Bosch first.

Tech specs

Below, I’ve put together a brief summary of the tech specs for the Vaillant EcoTEC Plus 637:

  • Boiler output to heating and hot water: 37kW
  • Ideal for: A large 5-6 bedroom home with 13 -16 radiators and a 200-litre water tank.
  • ERP rating: A
  • Guarantee: 7 years*


If you’re ready to replace your old system or regular boiler, but want minimal fuss or upheaval, the Vaillant EcoTEC Plus 637 could be the perfect choice. Its 37kW output makes it ideal for a large 5-6 bedroom home with high ceilings and 13-16 radiators.

Unfortunately this boiler will not fit in your kitchen cupboard or Edinburgh press, but it does still have a very impressive output for its size. I recommend fitting this boiler in a storage cupboard alongside your hot water tank.

Finally, Vaillant’s brilliant no-quibble 7-year guarantee and dedicated engineers mean you’ll be covered just in case you run into any problems later down the line. It’s just not as good a deal as some other boiler manufacturers out there!

*7-year guarantee is subject to being installed by a Vaillant-accredited installer and serviced Annually by a Gas Safe registered engineer.

What are your thoughts on the Vaillant EcoTEC Plus 637?
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