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This Main combi boiler is a nifty little boiler designed to fit in a cupboard and to be extremely simple to operate.

Here are some specs:

  • 29.5 kg
  • 70 cm high x 39 cm wide x 28.5 cm deep – a cupboard fit;
  • 0.5 cm clearance required on each side for servicing
  • Available in 25kW and 30 kW only
  • 5 years warranty

The important thing to note is that this Main boiler retailing at around £550 (at the time of writing) is identical internally to the Potterton Assure, the Baxi 600 at £800 and the Baxi 800 at over £900. So you get exactly the same boiler at a lower price. But you do get what you pay for in the end.

The differences are in the warranty periods: 7 and 10 years for the Baxi 600 and 800 respectively. The 800 also comes with a Magnaclean Micro 2 magnetic filter, so is a slightly better deal than the 600 as you get filter + 3 extra years of warranty for an extra £100. The filter itself is worth around that much.

Another small difference is that the two Baxi boilers come with a gap at the rear where you can run pipes. You don’t need to buy a stand-off kit separately for this purpose. The Baxi boilers also have a different filling loop.

Let’s get started with the pros and cons of the Main Eco Compact combi boiler.


Simple interface

The Main Eco Compact has an extremely simply interface, with only the ability to adjust the temperatures and a reset button. There isn’t even an on/off button or heating/hot water selector. It couldn’t be more bare bone than this. Some may see it as a disadvantage too and we look at this later on but this extreme simplicity is by design.

A thermostat will be required to control the heating as there is no other way to switch the heating on or off.

It’s easy and intuitive to be able to adjust the temperature with a dial instead of having to enter digital menus and sub-menus, then saving the changes. Each dial is clearly labelled as well. This is certainly a big plus.

In rented properties, there is little for tenants to get confused about and change settings by accident. This boiler is ideal for anyone who just wants to get heating and hot water and get on with life. There is zero learning curve to it.

The LCD display is a slight improvement and avoids all those old fashioned light indicators. Error codes are displayed on the display but the list is quite short.

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Pressure dial

The pressure dial is another plus. It’s right in front, always visible, and easily understood by all with green and red areas. I think the old-fashioned dial is better than the modern digital version where you may be presented with just a number or even have to select the right menu to find it. And if the boiler is off, there’s no way for you to know the pressure!


At £550 you’re getting exactly the same boiler as the Baxi 800 at over £900.

You do get half the warranty period but that’s for you to decide whether you’re prepared to take the risk, or pay a gas engineer for repairs. If you’re not going to service the boiler every year for 10 years, there’s also no point in getting a long warranty period as annual service is a condition of the warranty.

You also need to fit a magnetic filter these days for the warranty to be valid and the Baxi 800 already comes with one, so you need to fork out a little extra for a magnetic filter when fitting a Main. But filters can cost less than £50.

Remember, you’re paying over £900 for the same boiler with 10 years warranty, so this is not a cheap, budget boiler despite the low price.

Quality components

Brass hydroblock, instead of plastic like some other well-known and more expensive brands.

Stainless steel heat exchanger. This is not as good a heat conductor as aluminium heat exchangers but the metal is much less reactive and the waterways large, so less change of a blockage due to sludge.

The heat exchanger is also easier to access, inspect and clean as it opens at the front instead of the top.

The burner door seal is made of rubber that doesn’t need to be changed every time you open the heat exchanger or on a regular basis, unlike some other brands out there. Instead, you just change it as and when required depending on its condition.

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Attention to detail

This Main boiler may have an exceedingly simple interface but a lot of though has gone into the design of this boiler with various well-thought out features for engineers, making it a pleasure to work on.

The simple interface itself is by design as mentioned before.

The expansion vessel is located on the side rather than at the back and the valve sticks out at the top of the boiler, making it easily accessible.

There’s also plenty of space to work inside.

There’s a drip loop that collects any water from the air intake and directs it to the condensate trap. A drip tray at the bottom to guide water away to a low point so it can be easily drained.

On the PCB wiring side, there is a drawing imprinted on the PCB cover that shows the length of wire to be cut and stripped. Not needed at all but a bit of help for a neater job. There’s even a plastic tab that holds the cover open when wiring up.

Open Therm compatible

There’s currently a push in the industry for Open Therm use and this starts with compatibility.

Open Therm is a language used to communicate between boiler and smart thermostat and allows the thermostat to control the boiler in an advanced manner as opposed to simply switching the heating on and off.

More importantly, a boiler which is Open Therm compatible means that you can use any third party thermostat out there that uses Open Therm and you don’t have to rely on the boiler brand’s own thermostat. You have a far larger selection of models and price.

Compatibility is important these days. Thermostats are getting smarter and… dearer, like the Nest for instance. If you purchased one for your home today and moved houses tomorrow, you’d want to take it with you and you’d also want to be able to use it on the next boiler.

Compare this to the Vaillant and Worcester boilers that don’t use Open Therm and have their own proprietary connections. Fortunately you can still connect a Nest to either of them as it works on most, if not all, boilers. But you wouldn’t be able to use the Open Therm connections in the Nest and so you’d lose out on this feature.

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Before we get to the negative aspects, let me mention the only neutral point I could find on this boiler and this is the noise it makes whilst in operation. Like most modern boilers, it is not noisy at all. However, it is not extremely quiet either, like the Intergas Rapid which is so quiet it’s hard to tell whether it’s in operation or not.

So I can’t claim this as a positive point, yet it’s not noisy enough to be a drawback.


Dumbed-down interface

I may have said earlier that it was by design but some may still call it dumbed-down. There are no options whatsoever to this boiler and when you’re forking over £900 for the identical Baxi 800, you may think you’re getting short-changed. Some of those missing options include:

  1. comfort mode: pre-heating hot water
  2. on/off button to at least switch off the boiler
  3. range rating to match the heat output to the property
  4. summer mode: turning off heating
  5. fault history

To be honest, none of those features are essential in any way, otherwise the Main boiler wouldn’t be able to function effectively. But most other boilers on the market come with most of those features and people are used to them. The lack of range rating is a bit concerning as it helps make the boiler more economical.

Ariston boiler interface

Vaillant provides a wealth of status codes, diagnostic codes, fault codes and program codes. Intergas has an advanced parameters list to optimise the boiler setup. Here you’ll only get a few error codes to work with.

So if you like to fine-tune your boiler and like all the bells and whistles, you’ll get none of that here. Personally I think a boiler that is easy to use by everyone is a plus. Look at all the buttons to get wrong on an Ariston boiler if you don’t know what you’re doing.

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PRV afterthought

While the attention to small details is impressive, the PRV connection seems to have been thrown at it at the last minute. The connection is angled and at the back, making it an awful location hard to access. You can’t solder in situ either as there’s a plastic component on the connection. Why couldn’t Baxi place the PRV connection at the front where there is still plenty of space, and make the connection drop down vertically like the rest of the pipe tails? There’s also plenty of space internally for that, rather than an awkward angled connection.

Pipe tails size

The pipe tails supplied are too long and hit the wall – no allowance has been made for pipe brackets against the wall. This is a bit of a moan as all it takes is to cut the pipe tails to length, but why couldn’t they be supplied at the right size? Ravenheat has got it right.

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Rear piping

The rear spacing on the Main boiler has been blocked with a metal bracket at the top that serves no purpose. Remember, it’s the same boiler for the Baxi 600 and 800 which allows the pipes to run freely at the back. If you want to run the pipes at the back of the Main boiler, you need to purchase the stand-off kit which costs a mighty £70 for what is just a couple of metal brackets in white finish. What a rip-off. So it’s either this or run the pipes to the side and if space is limited, for e.g. inside a cupboard, it’s not possible.

Condensate trap

When it comes to removing the trap to clean it, they couldn’t have made such a simple job more tricky. Unlike other most other boilers where you can just unscrew the trap from the outside and rinse it, here you need to access it from the inside and remove the whole trap, including breaking the seal. There are 3 connections to be undone, meaning 3 places where water can leak when you’re moving the trap over the PCB. What a poor, poor design! Don’t forget that you need to fill the trap when putting it back in place, so there’s even more risk now of water dropping over the PCB. Is that what the designers really wanted?

Flue test point caps

When is Baxi going to change its cap design? The one on this boiler is no different. The problem with this design is that you twist to lock it in place but the plastic is very fragile and breaks easily if the cap is twisted just a bit too firmly. How hard is it to change it to a screw design?

Design flaws

As this is a newer design, more flaws will come to light over time. Here are a couple which must have been missed at the design stage. The flue cap that is so accessible on the outside also makes it less accessible to screw the flue to the turret. If the boiler is in a cupboard, there’s even less space.

The gas valve is situated right at the bottom of the boiler. The PCB panel is in the way when trying to unscrew open the inlet pressure test point on the gas valve.

It would be nice to have an electric cable already wired in, otherwise you need to make sure you have one available when installing the boiler.

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There are 4 issues I have encountered in many boilers, so they are not exclusive to the Main Eco Compact. Some boilers have shown initiative and addressed them.

Filling loop

I personally prefer a standard external filling loop rather than proprietary ones. What happens when the latter fails? It’s more expensive to replace. A gas engineer could carry a bunch of standard filling loops in the van to be used in installations and repairs. You can’t do that when each boiler has its own proprietary filling loop.

The filling loop supplied here is slightly fiddly to install as you need to get two pipes exactly parallel to each other. Baxi even recommends building a jig to get this right every time. Sounds like extra work for what should be something straightforward.

It’s still possible though to use an external filling loop here rather than the one supplied by Main. I just wish all boiler manufacturers use the standard one to make life simpler. In fact, they would not even need to supply it, so it would be cheaper overall. They try to pass it as a fancy feature but it’s not.

Is the auto air vent needed?

Many boilers come with an auto air vent. This is needed whenever the heating system has been emptied and filled again in order to remove any remaining air. It helps to protect the heat exchanger that would quickly overheat if filled with air. The problem with auto air vents is that very often they leak, usually as a result of sludge in the system. It would be nice to see the auto air vent replaced with a manual one like on the Intergas boilers. You just need to open it any time you’ve filled up the system. Any leak inside the boiler can result in costly repairs. This simple change would reduce a frequent source of leaks.

PCB panel location

The PCB location in Main boiler is a drop-down flap at the front, with the PCB protected below a cover. This is quite a standard set-up across boilers. The problem with that is that water flows down. When you’re making repairs on a boiler, you tend to work from the front. And what’s just in front of you and at the bottom? Yes, the PCB.

Ravenheat has thought of that and installed its PCB and electronic components in a box in the middle that can be easily moved to the side when working on the boiler. So not only is the PCB protected in its box, it’s not at the bottom and it’s moved out of the way. I’d like to see more boiler manufacturers do that. At the moment, PCBs at the bottom are a recipe for getting wet. Some cynics might even think it’s been done on purpose…

Ravenheat HE80 combi boiler with its electronics box lifted off the bottom
Ravenheat HE80 PCB box

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While we’re on the topic of PCB, an issue with the Main boiler is that the panel is hard to close when you’ve wired in the live supply and a thermostat. There just isn’t much room for both, leaving the panel to bulge out in places. The magnets on the sides of the PCB panel then have trouble making contact with the boiler casing and cannot keep the panel held up.

Why a metal flue?

Another suggestion is replacing the metal flue with a plastic one. Because of the Grenfell fire, flues in high-rise buildings must now all be made of metal, inside and outside, to reduce the risk of combustion. But this is not a requirement in houses and smaller flats and the flues were already metallic prior to the Grenfell fire. What was the reason for having a metal flue?

The inner flue on the Main boiler, through which the hot corrosive flue gases flow, is made of plastic. So this plastic can withstand high temperature. In fact, plastic can withstand more than 100 deg C. Aren’t there plastic kettles? Why can’t the outside also be made of plastic? The inner flue cannot be made of metal due to corrosion from the acidic condensate. In fact, when there is a leak from the inner flue to the outer flue, the latter eventually rusts away. It is also due to this risk of corrosion that Baxi required the white part of the flue not to be on show until recently, meaning the metal outer part is never exposed to the rain and will therefore not rust.

An outer plastic flue would solve all this corrosion issue while also being cheaper. Cynics would argue again that it’s done on purpose…


The Main Eco Compact combi boiler is a high quality boiler made of brass hydroblock and stainless steel heat exchanger, all at a bargain price. Simple interface with zero learning curve, attention to detail and Open Therm compatibility are additional selling points.

In terms of drawbacks, the purposefully blocked rear space, the overpriced stand-off kit, the awkward location of the PRV and gas valve, and the fragile flue test points are all areas of improvement.

Additional suggestions that could apply to most other boilers too are:

  • using an all-plastic flue;
  • moving the PCB away from the bottom;
  • using a standard external filling loop and;
  • using a manual air vent to reduce risk of leakage.

All in all, in my opinion, the positives outweigh the negatives. There is no perfect boiler out there and this one is a keeper. No wonder it is very popular.

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