So, six years ago, I strongarmed my Gas Safe guy into installing a Broag Remeha Avanta Plus 30S boiler. I travel a lot in northern Europe and see these things all over the place, purring away very quietly and seemingly, efficiently. Imagine my embarassment when 18 months or so into service, it starting displaying the dreaded E5 error code. After spending many hours on here, and elsewhere, we addressed all the usual culprits: replaced the gasket, ignition probes, etc. But, despite text book readings, the problem persisted, albeit intermittently. A few months back, the problem got markedly worse, to the point where the boiler refused to fire after reset. So, I ploughed through the manual for the umpteenth time and this paragraph jumped out: "If a room thermostat with an anticipation resistor is being used, (user level) parameter P5 should be changed from 0 to 1." Bingo! 30 seconds later, the problem that has dogged the installation for years, was instantly resolved. Some years back, I replaced the old Honeywell room stat with a digital DT90E, with its TPI circuitry. There was no mention in the paperwork, but it obviously requires the provision of advanced current. Rookie error? Possibly. RTFM: definitely. There are a number of morals to be taken from this tale and I brace myself to hear them. But, anyway, I offer this up, just in case it might help someone else who's in the same boat.