Hot water and old boiler

ThisIsWeird

Yazmina said:

Ectophile said:

Water going alternately warm and cold could be a clogged heat exchanger.  It will struggle to heat the water properly, and eventually overheat and shut down as it's failing to transfer the heat from the burner to the hot water flow.

It may then start cycling on and off trying to keep the water inside the boiler down to an acceptable temperature.

Is this worth repairing on a boiler so old?

Hard to judge. A blocked P2P exchanger should be a fairly easy task to replace, but part prices can vary a lot - I buy new-pattern, or recon ones for my glowworm for around £25, and can practically replace them blindfolded now I've done it so many times :-(
But a new genuine 'glowworm' part could easily be £130 or so, and I guess most GSs would insist on such a part.
And, we don't know whether that's your problem.
That Magnaclean has its top lid spanner on it. The reason I asked about when it was last checked, is if there is evidence of captured sludge in there, then it makes a partially blocked P2P more likely. But, we don't know.
Is there any chance you are DIYish enough to check it? Lots of info and vids online. But, you need to be happy to do so.
10-odd years is not 'old' for a combi, but it is 'getting there'. 
Sorry, it's a toughie.

Yazmina

We are definitely not that DIYish! We'll get someone out to look at it.  Thank you. 

FreeBear

A like for like replacement will probably cost £2500-3000 from the likes of Boxt. But if you are considering replacing it, I'd urge you to get a quote for a heat pump - Octopus are doing some pretty darned good quotes at the moment -> https://octopus.energy/order/heat-pump/