Boiler Talk with Kevin Sullivan: A merchant’s perspective – Navigating water pressure, CPDs and the efficiency trap

As the heating industry evolves, the gap between theoretical efficiency and real-world performance is widening. KEVIN SULLIVAN, Managing Director of Plumb Merchants Dublin, argues that successful installations in the city’s unique housing stock require installers to look far beyond the brand name on the box, focusing instead on water pressure, operating temperatures, and the legacy of old pipework.

As a small independent plumbing merchant in the heart of Dublin, I often get asked for my “insider take” on where the national boiler market is heading. To be perfectly honest, I don’t feel I could give you a sweeping, data-heavy guide on national trends. We run a supply-on-demand business; if a customer walks through our door looking for a specific brand, we either have the channels to get it or we don’t.

However, what I do have is a front-row seat to the daily challenges faced by installers and homeowners carrying out retrofits across the north of the city and beyond. And from where I’m standing, the conversation shouldn’t be about which boiler is “best,” but rather which installation is “correct.”

The myth of the ‘bad’ boiler

One of the most common questions I hear is: “Kevin, what’s the best boiler on the market right now?” My answer is straight: “I don’t believe there is such a thing as a truly bad boiler on the market today. Because of the incredibly stringent manufacturing conditions and environmental standards that brands must adhere to, every unit available today is manufactured to a very high standard. The baseline for efficiency is now so high that the gap between an “entry-level” model and a “premium” model isn’t necessarily about how much gas they burn to heat a litre of water.

Instead, the differences lie in the quality of the internal components and the additional “intelligence” or capabilities the premium versions have. But in terms of achieving basic efficiency, they are all good to a certain degree. The real variable isn’t the machine; it’s the environment into which it’s being fitted.

 

Breaking the brand loyalty habit

We find that, in general, installers are fiercely loyal to the brands they know. It makes sense—if you’ve installed 100 units of a particular brand, you know the quirks, the spacing, and the error codes. You’re confident!

However, this familiarity can lead to a certain hesitancy when presented with newer, perhaps more technologically advanced products. I would strongly encourage every registered installer to step out of that comfort zone and take advantage of the Continuing Professional Development (CPD) courses offered by manufacturers and distributors.

Whenever an installer comes back to us after attending a CPD on a new product range, the change in their attitude is night and day. They move from being sceptical to being comfortable. These courses are an incredible service provided by the industry, and in a world where technology is moving as fast as it is, staying “loyal” to a 20-year-old way of working is actually a risk to your business.

The combi conundrum: Tradition vs Modernity

In our neck of the woods, we almost exclusively deal with retrofits and replacements rather than new builds. This means we are constantly dealing with the “hot press” tradition.

Across much of Europe, instantaneous hot water via a combi boiler is the gold standard. In Ireland, we are still very much wedded to our copper or stainless steel cylinders. While we are seeing a massive shift toward homeowners wanting to swap system boilers for combis to reclaim that hot press space, it isn’t always a “plug and play” solution.

 

A boiler vet

When a person comes to our counter looking for a new boiler, we vet the request, asking why they are changing, what they are trying to achieve. If you move a family from a large stored water system to a combi without checking the incoming mains, you aren’t doing them a favour—you could be creating a headache.

 

Dublin water crisis: The 0.5 Bar reality

Perhaps the most significant issue we face in Dublin—specifically near us in Dublin 1, Dublin 3 and Dublin 7—is the “water variant”. Depending on the age of the dwelling and the specific street, incoming mains pressure can be excellent, mediocre, or, frankly, dire.

We have experienced incoming water pressures as low as 0.5 bar or 1 bar. To put that in perspective, 0.5 bar is equivalent to a 5-metre head of water. That is incredibly weak. Conversely, a few streets over, you might find 2.2 bar.

The issue is compounded by the “occupancy explosion.” Many of the houses near our store started life as single-family homes. Today, those same buildings might have five or six times the average occupancy. Yet, the supply is still the same old half-inch lead or copper pipe coming in from the street.

The supply has remained static while the demand has become overwhelming. Once you hit peak time—the morning shower rush—that supply is completely depleted. If you’ve installed a high-output combi boiler that requires a certain flow rate to trigger the burner, and the mains pressure drops to a trickle, the boiler won’t even fire. This is why we feel it is essential to vet every installation. Selling a high-value product that won’t operate adequately because of local infrastructure isn’t just bad business; it’s a disservice to the trade.

 

The Condensing Myth: The 67°C Rule

Every boiler we sell today is a condensing boiler, but it only delivers on its efficiency promises when it operates in condensing mode. This typically requires a return temperature of around 54°C or lower, which usually means setting the boiler flow temperature to approximately 67°C.

The problem arises when an occupant (or an installer trying to compensate for undersized radiators) turns the dial up to 75°C or 80°C. At that point, the boiler stops condensing. You’ve essentially paid for a high-tech, high-efficiency machine and then forced it to run like a 1980s cast-iron beast. It is a waste of money and technology. Part of the installer’s job now is educating the homeowner: “Keep the temperature lower, let the house warm up more gradually, and let the boiler do the job it was designed to do.”

Managing the legacy of the back boiler

We are currently in an era where we are trying to get new technologies to work on very old “bones.” Many Dublin homes evolved from back boilers to gas-fired central heating, then to wall-mounted units.

With modern controls, we are trying to get sophisticated zoning and smart tech to work on pipework layouts that were never designed for it. You can only deliver a truly comprehensive solution if you understand the entire pipe layout of the dwelling.

Current regulations require a certain level of temperature control and zoning. While zoning makes absolute sense from an efficiency standpoint, it isn’t always feasible in a retrofit unless the pipework allows for it. We see many “considerable extensions” being added to old houses where the original system was never designed to handle the additional load.

 

My advice to the trade

If I could leave installers with one takeaway, it’s this: The “box-swap” is dead. In the modern market, you aren’t just a fitter; you are a consultant. You have to be the one to tell the builder or the homeowner that their half-inch pipe won’t support a 40kW combi. You have to be the one to explain why the boiler temperature shouldn’t be set to “max.”

At Plumb Merchants Dublin, we will always have access to the stock and the brands to help you get the job done. But the success of that job depends on the vetting you do before you even crack a nut on the old system.

Let’s make sure the high-tech equipment we’re putting into these houses actually has the environment it needs to thrive.