Your heating bill has gone up and nothing in the house has changed.
Three things to check

If your heating bills have gone up and nothing in your house has changed, a lot of the time it comes down to one of three things. I am not going to tell you your boiler has broken down, because it is usually nothing like that. What tends to happen is that the boiler is working harder than it needs to, and the house is calling for more heat than it needs to, and none of that shows up as a fault. Everything still works. It just costs you more, and sometimes it takes longer to get the house warm.

Two of the three you can check and change yourself today without any extra help. The third one you will need a hand with, and it is worth knowing about because in the long run it is the one that costs the most.

One: the temperature the boiler
sends out to your radiators

The first one is a setting on the boiler itself, and it is not the thermostat on the wall. It is the temperature of the water inside the boiler that is being sent out to your radiators (flow temperature) to heat them up. You can normally see it on the boiler display, and there will be a dial or a set of buttons to adjust it.

If you have a combi boiler you will probably see two of these settings, one for the radiators and one for the hot water at the tap. The heating one is the one we are looking at here, so the radiators specifically.

If it is set very high, 75 or 80 for example, there is a good chance the boiler is not running as efficiently as it could be. A condensing boiler set to 75 or 80 is probably not behaving like a condensing boiler at all. Bring the same boiler down to about 60 or 65 and it condenses the way it was designed to, which is where the saving comes from. Most homes will still heat up perfectly well at that setting. They may just take a little longer to get there.

I have already made a video showing exactly how to find that setting and how to adjust it, and I have written it up as well, so I will not go through all of it again here: the 60 degree check, and how to set your boiler flow temperature. Of the three things on this page, it is the single easiest one to do and the quickest to feel.

One thing to be careful of. If you have a system or heat only boiler with a hot water cylinder, the water going into that cylinder has to get hot enough to keep it safe, which means over 60 degrees for legionella control, so the boiler setting on those systems is not the same conversation. Ask your engineer before you change it.

Two: what your heating is doing
while you are out

The second thing is the schedule. If nobody is at home, is the heating still coming on?

Go into the schedule and check it properly rather than glancing at it. Quite often somebody set it at some point and it has simply carried on since. It might have been a previous resident, or somebody else in the family, and they set it last winter and it has been running that way ever since. So you can be out of the house, or tucked up in bed, and the heating is still firing when nobody needs it.

While you are in there looking at the heating times, if you have a system boiler or a heat only boiler with a hot water tank, check the hot water timings as well. You know how much hot water your household actually uses. If there are only one or two of you and you do not need hot water across the whole day, you can set it to heat once or twice a day and leave it at that. If you have a bigger family and people are using hot water all day long, then keeping it on longer makes sense. The point is that the timings match the way you live now, not the way somebody lived here before.

Three: a
dirty system

The third one is a dirty system, and this is the one you cannot really sort out yourself.

Sludge in the system means your radiators take longer to heat up and never quite heat properly, which means the house takes longer to warm up, which means it costs you more every time the heating comes on.

The only real check you can do at home is to feel the radiators. If they are cold at the bottom and warm at the top, there is a good chance there is sludge sitting in them. That check does not work the other way round though. Radiators can feel fine and the system can still be dirty.

The better moment to find out is when the boiler is being serviced. Ask the engineer what the system is looking like, and they should be checking it anyway. When they clean the magnetic filter, or take a sample, they can tell you straight away whether it looks like a clean system or a dirty one.

We were at a property recently where the homeowner had had a fault fixed about a month earlier by another engineer, who replaced the pressure sensor in the boiler. We were called out because the boiler had broken down again. We changed the pressure sensor and cleaned out the magnetic filter. We found chunks of debris in the magnetic filter not just sludge. There was a lot built up in the magnetic filter as well which we cleaned out thoroughly. It was a very dirty system. This time we told the homeowner what we were looking at: the same thing is likely to happen again, and the way to deal with the cause is a power flush. We gave them the options and we gave them a price, and we left it with them. There is no hard sell from us. But we did say that there is a good chance the boiler breaks down again, and nobody wants that happening in the middle of winter.

So that is where the third one sits. You cannot fix it yourself, and I am not going to pretend otherwise. What you can do is know what you are dealing with, so it is a decision you are making rather than something that happens to you.

The short version

If your heating is costing more and nothing has changed, start with the flow temperature on the boiler, because a condensing boiler set at 75 or 80 is not condensing and 60 to 65 usually heats the house just as well. Then check the heating schedule, and the hot water timings if you have a cylinder, because a schedule set by somebody else is still running. If both of those are already right, you are most likely looking at a dirty system, which slows your radiators down and costs you money every time the heating fires. The first two are free and take an afternoon. The third one needs an engineer.

Quick answers