Considering a new boiler?

The boiler market is the largest in Europe by value, in 2010 it was worth over £1.3 billion and has obviously grown since then. Instantaneous Combination boilers accounted for 74% of sales in 2010, of which Combination storage boilers accounted for 3% of sales and heat only boilers accounting for 23%. Currently Combination boilers have over a 50% market share in the U.K. which is growing.

So taking this into account it is fair to say that Combination boilers are growing increasingly popular and seem to be the way of the future. It is also fair to say that the U.K. boiler market is large indeed and there plenty of people interested in your business.

I have created this page with the intention of providing customers considering a new boiler with the facts, and hopefully help in guiding them to making a sound decision when it comes to choosing a new boiler.

Now Im assuming that you definitely need a new boiler, but if you’re not sure then you might be best off having a look at my Do you need a new boiler? page first.

First of all there seems to be a misconception among customers that if they upgrade their old boiler then it has to be replaced with a Combi. This just isn’t true. From 2005 it was made mandatory for all gas boilers to be condensing to meet new emissions regulations. So it is true that if you want to install a new boiler today that it has to be a condensing “A rated” appliance, but it doesn’t have to be a combi.

Essentially there are three different types of boiler; the Combi, the Heat-only and the System-boiler.

The Combi boiler is an instantaneous water heater, which means it doesn’t have to heat up the water first and store it before it can be used – it heats up the cold water going to the tap as it passes through the boiler. A Combi boiler incorporates all that is needed (pumps, valves etc) inside the boiler itself.

The Heat-only boiler cannot provide hot water on demand, on this type of system you would have a means of storing hot water with a cylinder. The water in the cylinder has to be heated up first before you get hot water. The Heat-only boiler essentially just provides heat which is then circulated via a pump, directed via a valve or a series of valves to provide central heating and/or hot water. The pump and valves on the system have to be fitted external to the boiler and are usually located with the cylinder in the ‘airing cupboard’.

The System-boiler is essentially a Heat-only boiler, except it has a few of the extra components fitted inside the boiler. So a System-boiler would have the pump, pressure gauge and expansion vessel incorporated into the design. You still need the cylinder and valve(s) to direct the heat as needed.

Overall the Heat-only type of system is generally a more versatile system, albeit less efficient. If your boiler stops working then you generally have an immersion heat to provide hot water short term. With a Combi there is no immersion heater so when they stop working completely you have no central heating and no hot water. On the down side with a Heat-only system you are heating up water in a storage unit which goes cold eventually, so there is a small inefficiency there. With a Combi it heats the water on demand hence they are more efficient when it comes to delivering hot water.

Now when it comes to deciding between a Combi and a conventional system, it can be a decision easily made. The biggest drawback of a Combi is that you have to have decent mains water pressure and a good flow rate coming into the house. If the flow rate is insufficient then you will get a really poor flow from the tap. So in this situation it would not make sense to install a Combi, and a conventional system would be more suitable. Assuming you already have a conventional system then there is nothing wrong with installing a modern like for like High Efficiency replacement for the Heat-only boiler you currently have. Don’t be misled into thinking that you have to install a Combi because this just isn’t true.

Now everyone wants to save money on their gas and electric bill, but in most cases the old boiler you may have at present is probably more efficient than you think.
If you are considering upgrading your old boiler to a new High Efficiency condensing boiler to save some money, then this in most cases is a bad decision. In most cases it will probably take you many years to recoup the cost of the initial investment in a new boiler, before you start saving any money.

So if you have a problematic boiler regardless of its age, which is costing you money and breaking down constantly, then replacing it is a very good decision.
Replacing an old boiler, that hardly ever goes wrong and consistently does its job(in an attempt to save some money) is usually a bad decision.

If you are considering a Combi, or if this is what you have decided to go for, then avoid the types which have a built in storage tank of any sort. This would include Combi’s with a thermal store or and unvented cylinder incorporated. To be completely honest most of these aren’t actually proper Combi’s. On paper they are, but in reality most are essentially Heat-only boilers with a storage unit.
I give this advice because they tend to be more problematic than standard Combi’s, and when they go wrong they are usually more expensive to fix. Also if something expensive goes on the unit then it is often more cost effective to replace the whole unit. On a conventional system each component can be replaced individually, whether it is the boiler itself or the cylinder etc.

Insurance companies won’t insure them

There used to be a time when insurance companies would insurance any boiler you might have had. They have wised up to this recently and most will not insure a boiler with a built in storage unit. Also British Gas I know for certain have started excluding certain boilers regardless of their type. I’m sure the other insurance companies are doing the same. So this is another good reason to avoid a boiler with a storage unit.

What make of boiler?

There is a lot to choose from. It seems each installer has their own preference, but I will narrow this list down and make it really easy for you.

Personally if I was installing a new boiler there are only three manufacturers I would consider at present. Worcester, Vaillant or Baxi. I wouldnt give anyone else advice I wouldn’t take myself.

I have based this decision on several factors. Value for money, overall design, inherent design flaws and how often I have to repair them and the cost of replacement parts. It is important to note that there is not a single boiler I have ever come across which is perfect and doest have any design flaws.


I think the fundamental design of these boilers is good, and when this is the case, the reliability and life span of a boiler is generally determined by the quality of its peripheral components(fan, gas valve, pump etc).

If I was going for a Combi then I would probably choose the Baxi Duo-tec or the Baxi platinum, both are seemingly built to last. I think its fair to say that a manufacturer probably wouldn’t offer a 10 year warranty on a boiler, if they didn’t think it was built to last

Both are essentially the same boiler as far as I know, but the Duo-tec at present comes with a 7 year warranty and the Platinum comes with a 10 year warranty. These boilers are built very well, there is not much use of plastic on these boilers and the hydraulic blocks are all made of brass. I don’t like the range of Heat-only boilers Baxi has to offer, so there isn’t one I would recommend.

I have come across some of these boilers that are 7 years old that have never been services or looked at since they were installed. Of the ones that were working well they were in near enough perfect condition and working as well as the day they were installed. I have come across many that have been in very poor condition, that have not been maintained very well over the years that have suffered mainly due to installation defects. The installation defects aspects is something I will mention a bit later on.


If I was going for a Combi or Heat-only boiler then this is another one I would consider. I like the Worcester Greenstar Junior, I think this is a well designed boiler and offers quite good value for money at present. The 28 kw version is roughly the same price as the 28 kw Baxi Platinum but only offers a 5 year warranty at present. So I think the Baxi offers better value for money.
If I was considering a Heat-only boiler then I would definitely be looking at something in the Worcester Ri range.
The only complaint I have with the Worcester is that they have made the mistake of incorporating a lot of plastic into the design. Having said that they don’t go wrong very often, when they do the parts of reasonably priced in general. From an engineering point of view when you look at the Worcester and work on one, you can tell that it is a well thought out design and someone has put a lot of thought into the design.

On the Juniors they had a problem with the left hand hydraulic block which would pinhole and leak. I’m not sure if they have fixed this issue on later models but this is obviously why brass hydraulic blocks are better. Also the expansion vessel which regulates the system pressure is right at the back of the boiler, and if this needs replacing you either have to remove the boiler from the wall to replace it, or fit an external one somewhere on the pipework. To date I don’t think I have come across one which needed a new expansion vessel. I believe it is on the Worcester CDI models where the expansion vessel is located inside the boiler casing and can be easily replaced. The CDI models are a few hundred pounds more though. Taking all this into account I would still most definitely consider a Worcester.


Vaillant have been making boilers for a long time. They actually invented the first Combination boiler around 1966 i believe. So in theory they should be market leaders and I don’t think they are far off to be honest. The Vaillants are seemingly built to last. These boilers are very good indeed.
I like the older ones a lot. If I was considering a Combi then like I said the Baxi would probably be right at the top of my list for value for money.
The Vaillant equivalent is a fair bit more expensive than the Baxi, at present I believe most Vaillant’s come with a 5 year warranty. I have been led to believe some come with a 7 year warranty, but I’m not sure if this is true or not.

As I said previously most installers have their own preference as to what boilers they would recommend. Their reasoning for their recommendations varies. I have tried to justify the reasons for what I have said about the boilers I have mentioned.

Installation defects and your manufacturers warranty

When it comes to installing a new boiler then the installation should be done properly. I come across a lot of boilers with issues which are created by installation defects. It tends to effect Combination boilers more because most have intricate plate to plate heat exchangers designed for efficiency when delivering hot water. These heat exchangers can get blocked up very easily with ion ore particles etc that have been left behind in a dirty system that wasn’t flushed out properly. Problems with the hot water are often indicative of a dirty system.

So when getting a new boiler installed make sure the installer flushes out the system properly. If you are upgrading a really old boiler like a back-boiler for example then a power flush is usually imperative. If your system if power-flushed then get documentation from the installer that he has done this. Your warranty is usually void if the manufacturer suspects a dirty system and you have no way of proving it was flushed.

Also I would recommend the installation of a magnetic particle filter, such as the Magna Clean filter for example. These are relatively inexpensive and most cost under £100. These are fitted on the return pipe of the central heating system, and they do a good job at removing any little metal particles left behind that would otherwise go through the boiler and potentially cause damage.

So just to summarize

If you have decided to go for a Combination boiler, then avoid the boilers with a storage tank of any sort – most insurance companies wont even insure these now. If you want stored hot water you’re probably better off with a conventional system.

Make sure your system is power flushed properly before installation. Get documentation from your installer as proof of this for your warranty. A power flush isn’t always necessary but if you have one done you cant go wrong.

Avoid the manufacturers I have listed below. If you go with something reputable like the ones I have mentioned above then you shouldn’t go wrong. The more reputable manufacturers tend to offer the better products, better after sales support, better technical support to engineers that have to fix them when they go wrong, and spare parts are usually more reasonably priced.

The ones to avoid…

There is a lot to choose from. If you are struggling to make a decision on what make or model to go for, then this may help as I have made a list of the ones that I would avoid at all costs. I think if you avoid rubbish like most of the stuff listed below then you cant go too wrong. These are listed in alphabetical order. Words cannot describe my disdain for most of the boilers listed below, but at the same time they keep me in business(fixing them not installing them!).

Most of the boiler manufacturers that offer cheap boilers make their money on the sale of spares, and not on the actual sale of the product. I think that when this is the case, the product doesn’t usually offer very good value for money.


Not that common, the ones I have come across have generally been simple faults and nothing major, but these in general are cheap B & Q specials.


Once again most of the older ones were not too bad. They had their issues but I think most of the older ones were definitely a cut above the average B & Q special. The company I used to work for were agents for Alpha. I often went out to repair brand new boilers that were days or even a few weeks old and have failed. These were of the Intec Range. Most of the time it was important components like the fan, PCB etc that would fail. Sometimes it was more simple like the hot water flow switch for example. But when major components like that fail so early on it is indicative to me that these are built with cheap components and wont last. I would avoid the Intec at all costs.

Baulter Buderus

These are quite rare. I have worked on a few of them. Baulter Buderus Techincal support is rubbish. Their boilers were seemingly designed by children and have a lot of plastic incorporated into the design like the combustion cover. These look and feel cheap and nasty. Parts were not that commonly available at one point, I have seen people suffer in the cold whilst waiting upon the delivery of parts. I believe it is a common problem on these where the primary heat exchanger fails and cannot extract heat from the burner properly. This causes the flue thermostat to operate as the flue gases are too hot. I have only personally come across this problem once, however I believe this is a common problem as I spoke to an N Power quality inspector once, who said they had a competition to see how quickly one could replace the heat exchanger. So taking all this into account I would avoid these.


Probably the most common of these that I come across is the Biasi M90 range. These are essentially based on the Ideal Mini range with some slight differences. These in general are trash. The cost of replacement parts are expensive.


In the world of cars, the French seemed to have filled the quality gap between the Italians and the Germans. In the world of boilers however, the French ones are just as bad as Italian ones. These are rubbish, I would avoid them.


These are trash. Some of the older ones like the Modena weren’t too bad but the new ones are diabolical. Seriously.


Some of the older ones were not too bad actually, like the Halstead ace for example, but in general these aren’t built to last. They’re cheap to purchase but when they go wrong(and like all boilers they do) the cost of the parts can be extortionate. I have come across some of the older ones where a simple printed circuit board costs in excess of £500. In general they make their money on the spares not the actual purchase of the boiler.


I have only ever come across one of these, I serviced it. It looked like it was going to fall apart so I was very careful. Very rare, I don’t think anyone would recommend one of these.


I have only ever come across two or three of these, also very rare. I think most I came across only needed simple repairs, I remember replacing the ignition printed circuit board on one. If it looks cheap and nasty, then it probably is. If you like the sound of a Jaguar but want something thats just as bad but sounds a bit cooler, then might I recommend the Italian made Lamborghini. Unlike the actual sports car, the only thing fast about these boilers is the rate at which they fall apart.


I’ve only come across literally one or two of these. One needed a printed circuit board. I think they do mainly commercial boilers, not sure though. If it looks cheap and nasty, then it probably is…


As far as I know most of these boilers are essentially Vokera models. Some have slight differences but are near enough identical. These are cheap, they fall apart and they make money on replacement spares. A definite B & Q special.


Not much to mention regarding this. Most engineers don’t like working on them. They are trash.


Not that common. I don’t like the design, theres too much plastic. I think Remeha produce mainly commercial boilers, which I have been led to believe are quite good, but I would avoid the domestic ones. I’ve also been led to believe their after sales support is quite good, straight from the mouth of a customer but I would still avoid these.

Saunier Duval

Another great French boiler. Or not. I believe Glow worm now owns Saunier Duval and a lot of their products are identical or very similar, the older boilers are anyway. Lots and lots of plastic and expensive parts. Not good.


Same again, these aren’t built to last. They’re cheap and nasty. Parts aren’t cheap. Lots of plastic that goes wrong. The Sime PLanet Super 4 W.M is probably one of the worst. These look cheap and nasty, and most definitely are.


I think I have only ever come across one or two of these. It was crap. I believe Trianco manufacture mainly commercial products but do some domestic ones too. I doubt anyone would recommend one of these.


Some of the older one are actually quite good. The Vokera Linea is one such boiler. Things really went wrong when they started making condensing boilers. The Vokera Syntesi is one such boiler which is absolutely diabolical, it was essentially a Linea which had been redesigned as a high efficiency condensing boiler. Replacement parts in general aren’t cheap. The new ones are really bad. If Ive ever come across a really poor design it has to be the Vokera Mynute. The new boilers they have to offer just fall apart.

The warranty

Aren’t Combination boilers rubbish?

This matter seems very subjective. Personally I Like Combination boilers, I think they are compact and neat and are a very clever idea. There is no such thing as a perfect system and nothing lasts forever. On a conventional system with a Heat-only boiler there are various components that are external to the boiler itself. These include pumps, valves and expansion vessels etc. So when something stops working it could be the pump or a valve external to the boiler.

When something goes wrong with a Combi, everything is inside the unit and it would obviously appear that the fault is with the boiler itself. I think this has given customers the general point of view that when the heating or hot water stops working that it is the boilers fault.

At the same time there are good products and bad products. A lot of the time customers are ignorant as to what is good or bad and go on the advice of their installer. If their installer is ignorant then they will most likely install anything, often going with whatever is cheapest at the time.

If you have an ignorant installer then there is a good chance the product they install wont be installed properly. Not flushing a dirty system out before installing a Combi is one such example. Not insulating the condensate pipe properly on a condensing boiler is another one. These issues often reduce the life of a boiler which wasn’t built to last anyway.

A dirty system is particularly bad for a Combi boiler as the heat exchanger(s) inside these boilers are very intricate and can get blocked easily. A dirty system takes its toll on pumps and valves. Automatic air vents cannot seal properly and often start to leak as a result of a dirty system. Most of these issues obviously affect regular boilers too, but I’m just trying to make a point.

Condensing boilers

There is a misconception about condensing boilers. Lets just clear this up quick for anyone who cares.

Any boiler can be condensing, whether it is a Combi boiler, Heat-only boiler, System-boiler or even an oil boiler. Baxi now even do a high efficiency condensing back boiler with an electric fire on the front. Making a boiler condensing is a means of making it more efficient. Since 2005 all new boilers in the U.K. had to meet new emissions regulations and in order to do this they had to be condensing.