Estimated boiler repair costs in SE14 range from the cheapest Boiler repair £80 (G&H Gas and Heating based in SE6) to the dearest Boiler repair £200 (RD plumbing and heating services ltd based in SE15). This is an average cost, replacing a heat exchanger will be more expensive, a diverter valve less so.
Comparing gas heating engineer estimates for boiler repairs in SE14 gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
What to do - If your boiler is playing up, quickly get rates and quotes for boiler repairs by clicking "Get quotes" to post your job to heating engineers in SE14

"Boiler repair, replacing pressure relief valve"
SE8
"Boiler repair - replace pressure relief valve. We have already had the expansion vessel replaced."
SE16