The upstairs in my semi-detached home is noticeably colder then the downstairs in this weather with the heating on full, the downstairs has nice big double radiators, the upstairs has a selection of small single radiators and a towel rail in the bathroom. All windows are an older style double glazed unit.

How can I identify if my coldness issue upstairs is either a lack of heat coming from the radiators or what heat the radiators are putting out is escaping through my old windows, supposed insulated walls and insulated ceiling?

I was thinking of renting a thermal camera and the camera would show me the cold spots to indicate where heat isn’t reaching or spots where the heat is escaping through walls, ceiling or windows?

Have you tried bleeding the upstair rdiators, and looking at the water that comes out to see if its full of muck?

if the upstairs rads are as hot as the downstairs rads, but the rooms upstairs are cold, then you can pretty much say they are undersized.

No, but I can try that, the boiler is only a couple of years old and has been serviced each year to maintain the warranty, there is a system filter fitted.

are the upstairs ones full of air.

If the insulation in the loft is sufficient and the system is otherwise new and well maintained you can try bleeding and balancing the radiators. Balancing is often forgotten and can make a big different.
If that all fails then the rads are too small – maybe they put in smaller ones as traditionally we wouldn’t spend much time in the bedrooms and I know one of our rooms is a bit chilly for the office work we now do in it but it would be fine for sleeping and dressing in.
There are some online calculators to assess how big a rad you need – just measure yours and compare with equivalent in Screwfix website and check the BTU output against what you should have.

BTW heated towel rails are useless for heat output unless they are massive. And even then they don’t convect heat much. I have a big column rad in my bathroom with a towel rail above it which works very well.

How can I identify if my coldness issue upstairs is either a lack of heat coming from the radiators or what heat the radiators are putting out is escaping through my old windows, supposed insulated walls and insulated ceiling?

Is this a new thing or has it always been as such?
In general bedrooms are supposed to be a bit cooler than downstairs so they tend to have single rather than double rads – but that can vary. Heat rises so the bedrooms should benefit from heat rising from below through the floor.
Check the rads for air and feel all over for heat – hot at the top but cool at the bottom might indicate a restriction in the rad.
Have they been turned down for some reason?

If your CH pump has multiple settings you could try running it at the highest setting to see if that changes anything (it’s just a lever or dial on the side usually).

Assume the upstairs radiators are working? ie, hot top to bottom with no cold spots.

Can you feel any cold spots with your hands on the walls/ceilings? What about the loft hatch? It’s amazing how much heat you lose through a poorly insulated ceiling and loft hatch.

Hiring thermal imaging sounds awesome, but might be overkill. For under £20 you could buy one of these and look for cold spots?

It could be that your upstairs radiators are not large enough, but my money is on too much heat loss somewhere. Pretty sure there are calculators online to help you figure out what size radiator you need for any given room.

Look for drafts etc. It’s the opposite in our house, roasting upstairs, and we’ve small rads in each bedroom. Made ‘hotter’ recently by boarding out the roof – really has increased the insulation. We only have 3 radiators downstairs, one large one in the open plan lounge, one in the kitchen and one in the downstairs loo.

If the upstairs rads are hot, then your either losing the heat or there are drafts.

Check your TRVs downstairs aren’t fully open. Although not always very accurate, they shouldn’t be fully open..

Non contact thermometers are cheap and readily available these days, since the world started pointing them at each other’s foreheads. You’ll be able to judge if the rads are even temp across their area, and to look at cold spots on the walls and ceilings, without having to get tools out or make a mess.

I’d guess if your house needs big doubles downstairs, it likely needs them upstairs too.

Are the upstairs rads cooler than the downstairs ones if not then you should be able to rule out sludge/bleeding etc.

I’ve thought about buying/hiring a thermal camera myself in the past but it’s hard to get a frame of reference (my neighbours houses are different styles). But it probably would show up any obvious problems (although might be better to look at someone actually qualified to do a survey so you get more definitive results – but I imagine there’s a lot of cowboys in that field so good luck…)

Is the upstairs cold to the point you actually need to do something about it (as others have said upstairs rooms are generally cooler)? Or is it a couple of weeks a year where it’s a bit nippy but you can cope with it easily enough? I only ask as whenever I get to the point of thinking about changing rads/double-glazing in winter or fitting a/c in summer I’m usually reminded it’s a lot of money to spend to fix a very minor issue in the scheme of things.

I’ve thought about buying/hiring a thermal camera myself in the past but it’s hard to get a frame of reference (my neighbours houses are different styles)

Any moring where there is a frost you can see who hasn’t got much loft insulation as the frost on their roof melts first. The last one with frost left either has the best insulation or doesn’t use central heating…..

You could try closing the lockshield valves on the downstairs radiators very slightly to force more water through the upstairs ones.

It’s probably a rad balancing issue, could be air, unlikely to be undersized rads as heat will be rising from below so they need to do less work. I have 9ft ceilings poor insulation and stone walls, the upstairs rads are smaller than downstairs and perfectly fine

Any moring where there is a frost you can see who hasn’t got much loft insulation as the frost on their roof melts first.

or is growing weed in the attic.

I’d check the balancing if the upstairs rads seem cooler than downstairs. (Google it for full understanding) And don’t mess with the lock-shield valves until you understand the basic idea.

The premise being that the rads closest to the boiler will have the lock shield valves only slightly open to prevent all the central heating water taking a shortcut back to the boiler. The rads furthest from the boiler (in terms of pipework length) will have the lock-shield valves fully open.

A balanced system still have a specific temperature drop between the in and out of each radiator, that is fairly even throughout the house.

Of course when adjusting these, you need to have the user adjustable valve fully open.

Have you checked the pressure in the system?

Octopus energy let their customers borrow an infra red camera thingy for a week for free. Its very interesting, we found a massive swathe of cavity wall insulation was missing as well as where a window was blocked up.
Are you or any friends/family octopus customers? Seem to be a genuinely decent company.

I had under sized single panel single fin rads at my house upstairs when I moved in. Swapped them for type 22 of a similar size and changed the 10mm feed pipes to 15mm. Made a big difference.

BTW heated towel rails are useless for heat output unless they are massive.

After buying a chrome towel rail I read some interesting info (can’t remember where now) that Chrome ones have significantly lower output compared to white ones, apparently the chrome plating is really inefficient at radiating heat. 30% less for a radiator, possibly more for a towel radiator as it’s got a lot more surface area than a radiator.

Close curtains, and tuck them down the back of the radiator. This way the warm air isnt being drawn across the cold surface of the glass.

My house can get reasonably warm, its been insulated in the walls, i have the double glazing at the back(this year for the front to be done) what I really notice is in the bedroom when i tuck the curtains into the back of the radiator, the heat is increased substantially.

Them little non-contact thermometers – you need to be quite close to what you are measuring for accuracy over a small area. The laser pointer is just indicating the middle of the measurement area, which gets much larger as you move away.

There should be a diagram on the side of it to show this distance/size ratio.