Is it worth keeping underfloor heating in an uninsulated old flat?

[ScienceTeecher]

I really need some advice. I have just moved into an old flat which has water UFH and it was actually a big reason I bought the flat. However now I find out it was retrofitted without insulation so it does not get very hot. I havent been able to test it yet in this hot weather but a neighbour told me it had never worked well and the previous owner just spent a fortune to heat the water to 65deg setting and it still did not get up to a decent room temperature. It didnt help that he had thick carpets throughout. Now I have to choose to maybe try and add the insulation but that seems very expensive as the wood floor boards would have to be pulled up again, and the pipework might get damaged being moved.

Or I put radiators back in which seems cheaper..and makes me want to cry!!!

Is it worth keeping the UFh??

Try using it first. See if you can work out whether it is under a suspended wooden floor on metal plates or if it is embedded in concrete.
You might be ok. Heat always rises and underfloor heating needs to be left on a constant temperature pretty much all the time. It can take several hours to heat up if is a concrete embedded one or even 24 hrs in winter. If its concrete it will take longer to heat up and cool down but the carpet is less of an issue. If its a suspended floor, there isnt a heat sink so the carpet will block the heat and it might escape through the under floor void via drafts ans gaps before it can come up through the carpet.

Agree with @Geneticsbunny
it's best and most efficient to run it at a lowish temperature permanently than turn on and off.
The Carpet will be absorbing the heat so I would lift that and add a few thinner rugs before making any decision. I'd actually suggest you live with it through the winter and don't make any rash decisions just yet.

If the heating still isnt good enough , insulating the roof, windows and if necessary, walls, may be enough to fix the issue.

Its on aluminium spreader plates in a 10cm height void (i measured!) suspended above a concrete base. I assumed the air gets heated , but then the heat has to get through the carpet. I dont want to buy a new low tog carpet yet in case I have to abandon the UFH, so is tricky to test it over winter.

Why Isn't it expensive to leave it on 25/7 in the winter?

It takes 12-24 hours to heat up, so you will never be warm at the right times if you turn on and off. Also, by keeping the fabric of your home warm at all times the whole place will feel warmer all of the time. It will cost less to heat because its constant not massive peak and massive dip.

The only was to understand if it is properly working is to live with it over winter, and without the carpet. Can you put that in storage or something?

Also look at magnetic secondary glazing for your windows. thats cheap and easy and very effective.

Spreader plates are more responsive to being turned on and off than concrete and insulation underneath is less important than for concrete.

The reason it isnt that expensive to run is because the water it heated to a lowish temp like 40oc, that goes around the underfloor pipes and comes back to the boiler at like 30oc so the boiler only has to heat it up a little bit to be able to send the water round the loop again. If you turn it off, it has to start from room temp water again.
We have both types and they both need to be on all winter, although you can set a slightly lower temp overnight. So i think our room temp is 20 vs 15 at night.

Spreader plates are more responsive to being turned on and off than concrete and insulation underneath is less important than for concrete.

thank you, you have made my day.. there is hope!