Baxi duo tec combi he boiler lukewarm water- boiler 13 years old

yes get a new boiler,more efficient.

Probably need a new water to water (plate) heat exchanger. £120 ish plus £80 fitting cost. Is it worth a boiler change? First call up Baxi to find out if they still support that boiler with parts. If they do stick with it, if they don’t probably time to let it go. A bit of advice on having a new boiler fitted - buy a boiler yourself and have the gas fitter connect it up. You’ll probably save yourself a couple of hundred and also don’t forget almost every plumber will advise you to change an oldish boiler for a new one on the basis it will be more economical. It will and will probably save you £30 per year. Divide the cost of a new boiler by that and you get an idea of how long it takes to break even. Boiler replacement is the big deal for plumbers, you rarely get unbiased advice. Guy That

Diverted valve not fully changing over to hot water or if your in a hard / semi hard water area and no scale reducer fitted new heat exchanger or can be cleaned by chemicals ....

New boiler may be the best option’ but if you don’t have the money for that try a new hot water thermistor first they are not dear and it may just be that. ( a thermistor controls the temp of the water. It’s not the heat exchanger