If you’ve opened your latest gas bill and done a double take, you’re not alone. One of the most common questions we hear from homeowners is, “Why is my boiler using so much gas?” Higher usage isn’t just about cost. It can point to inefficiency, wear and tear or a system that’s struggling to keep up.
If your boiler is older or constantly running flat out, it could be time to upgrade your boiler. But before jumping to that conclusion, it’s worth understanding what’s normal, what isn’t and what you can do about it.
Warning signs often include radiators taking longer to heat up, the boiler firing up more frequently than usual, uneven temperatures around the house or hot water running out quicker than it used to. Let’s break down the most common causes and what you can realistically fix yourself.
Common reasons your boiler is using too much gas
An old or inefficient boiler
Boilers over 12 to 15 years old are usually far less efficient than modern condensing models. Back when many of them were installed, efficiency standards weren’t where they are today.
I still come across non-condensing boilers in houses around Navan and Blanchardstown that are doing their best but burning far more gas than they should. Even if they’re working, they can be operating at 70 percent efficiency or less. That means a chunk of what you’re paying for is literally going up the flue.
Poor boiler servicing and maintenance
A boiler that hasn’t been serviced regularly will become less efficient over time. Burners get dirty, components wear out and settings drift.
I’ve been to plenty of rental properties where the tenant says the heating is expensive and sluggish. Nine times out of ten, it hasn’t been serviced in years. A simple clean, safety check and adjustment can make a noticeable difference to gas use.
Thermostat or controls set too high
This is more common than people think. If your flow temperature is cranked up higher than necessary, your boiler will burn more gas to reach it.
Likewise, if the room thermostat is set to 23 or 24 degrees all day, the boiler will constantly fire to maintain that level. Most homes are comfortable at around 18 to 21 degrees depending on the room.
Heat loss from the property
Sometimes the boiler isn’t the real issue. The house is.
Poor insulation, single glazing and draughts will make any heating system work harder. If heat is escaping through the attic or gaps around doors, the boiler has no choice but to keep running. Older homes in Leixlip often benefit from relatively simple insulation upgrades that ease the load on the heating system.
Hidden system problems
Sludge in the radiators, partially blocked pipework, faulty pumps and leaking pressure relief valves can all increase gas usage. When circulation isn’t right, the boiler runs longer to achieve the same result.
Cold patches on radiators or noisy pipes are small clues that something isn’t quite right.
Simple checks and fixes you can try today
Before booking an engineer, there are a few practical steps worth taking.
- Turn your thermostat down by one degree and see if you notice a difference in comfort. Most people don’t, but the savings add up.
- Check the boiler pressure. It should typically sit between 1 and 1.5 bar when cold. Too low and it won’t run efficiently.
- Bleed your radiators if they have cold spots at the top.
- Review your timer settings. Heating empty rooms all day is money out the window.
- Lower the flow temperature if you have a modern combi boiler. Many are set higher than needed by default.
Even small adjustments can reduce unnecessary gas use without affecting comfort.
When to repair vs replace your boiler
This is the big question.
If your boiler is under ten years old and generally reliable, a repair or proper service is usually the sensible option. Replacing parts like pumps or valves can restore efficiency without the cost of a full new system.
But if you’re facing repeated breakdowns, rising gas bills and expensive parts on a 15-year-old boiler, replacement often makes more financial sense long term. I’ve had plenty of honest conversations with homeowners where the repair cost was approaching half the value of a new, far more efficient unit.
For homeowners in Navan, Blanchardstown or Leixlip, local property styles and ages vary, so the right answer often depends on how well insulated the house is and how the heating system was originally designed.
How to reduce gas usage and improve efficiency long-term
If you want lasting savings, think beyond the boiler itself.
- Upgrade insulation in the attic and wall cavities where possible.
- Install smart heating controls to heat rooms only when needed.
- Balance your radiators to ensure even heat distribution.
- Book an annual service to keep the boiler running clean and efficient.
If your system contains older pipework, a power flush can sometimes restore proper circulation. It’s not always necessary, but in sludge-heavy systems it can make a dramatic difference.
And if your boiler simply isn’t efficient by modern standards, upgrading to a high efficiency condensing model will usually reduce gas consumption noticeably, especially in family homes where heating and hot water demand is high.
When to call a professional
If your gas usage has spiked suddenly, your boiler is making unusual noises or you’re noticing inconsistent heating, it’s time to get it checked properly. Gas appliances aren’t something to experiment with.
A qualified engineer can test combustion, check system performance and advise whether a service, repair or replacement is the most sensible next step.
At Intec, we regularly help homeowners and landlords track down the real cause of high gas bills and get their heating systems running efficiently again. If you’re concerned about your boiler’s gas usage, contact our team today and we’ll be happy to advise on the best way forward.
