You have a lot of mixer taps /showers.
Check the temp of the hot water pipe coming out of the boiler.
You could well have cold water mixing in with the hot somewhere along the line.
I think these boilers are generally worth repairing.
Most parts are still availlable and mainly cheap.
Of course it wont be as economical as a new condenser in gas bills alone however no new boiler will last the 25 years plus that these old beasts have.
Two monoblock mixers downstairs. One bathroom upstairs with a monoblock on the basin and a thermostatic bath/shower diverter mixer, wouldnt say was excessive?
How would I check the temp coming from the boiler accurately? I know the routes of all pipes within the house. I'm not sure how cold water could be "mixing" in somewhere?
Closest HW take off (shower/bath) is only three lagged meters of 15mm copper away...