OK you have a heat only boiler and a cylinder.
Your current boiler is a fairly old one but simple and fairly reliable although the PCBs and fan will fail every 10 years or so and cost about £130 each plus fitting.
Tony
Its certainly old (26years) and even more basic than the one you described. In fact its hasn't a fan nor functioning PCB's (the pump overrun circuit was never activated).
A modern condensing boiler will save about 25% on the gas bill. Your gas bill will be about £625 pa and so would give a saving of about £160 pa.
Modifications are required to convert a simple installation like yours and will then result in a much reduced hot water flow rate.
I always recommend a cylinder storage system be retained as it gives so much better hot water performance.
To simply replace the boiler with a new heat only would be close to £1500. But that will only give you an 11% return on the capital cost. Fitting a combi would reduce the hot water performance and reduce the saving to about 6% so even worse.
So my advice would be to either repair the Solo or replace with a heat only.
Your Solo is pretty reliable and could go on for several years, but even at £350 would still be a better deal for a few years although ultimately it will need replacing.
I do hope he has correctly diagnosed the gas valve as at fault. Did he say exactly what he thinks has failed on it?
Tony
Thank you for that contribution. I hadn't given too much consideration to cost savings, concentrating more on getting it sorted. On reflection, our HW usage is low (2 occupant house) shower used in preference to baths. Typically the water is set for an hour run early in the morning and that cylinder full covers our needs for most of the day, if fact fairly often we are out all day and it never gets used. Not very efficient but that's the downside of an indirect system.
Incidentally the Gas engineer is happy to supply a like for like replacement with the same footprint as the old one and minimum pipe disruption, I think he said that would be circa £1600 with a 5 year guarantee. He is not pushing for a sale but mentioned the Vaillant as a worthwhile option.
Regards,
Benny.