in Jan 2018 I also had the dreaded F76 fault code appear on our Vaillant ecoTEC 630 +. I was also able to restart /relight boiler on a few occasions which stayed on for progressively shorter periods of times over a couple of days. I called out local heating company who claimed Vaillant 'accreditation' and who diagnosed (correctly) a failed thermal fuse which is not a replaceable part (for safety reasons). I was advised that the heat exchange needed to be replaced with an estimated cost of replacement at over £1k inc parts/labour. He then advised me that a new boiler was my best option (@ £1.6K -£1.8k inc fitting).
Anyway I decided to get a second opinion from Valliant directly. I told them the boiler was already broken and to my surprise they were happy to offer me their Platinum breakdown cover @ £250 for 6 month cover which covered me for any repair required up to a total of £1500 during the 6 month period. Needless to say I almost bit their hand off and I signed up.
The Vaillant engineer came out within 24 hours , he replaced the heat exchanger, upgraded a number of internal pipes as a preventative measure , he replaced the water pressure/flow sensor , he replaced the 10 liter expansion tank which wasn't holding the required 1 bar pressure ,he swapped out the (unreliable) Wilo pump for a (more reliable) Grunfoss pump and he recommissioned the system all in less than 2 hours. Had i purchased all these parts individually it would have cost me in excess of £800 and the fitting/labour would be in addition. So I have almost an entirely new/reconditioned boiler and all it cost me was £250. I am delighted with Vaillant beyond my wildest expectations. Their customer service was outstanding.
My (maybe cynical) view now is that I think that most local heating companies are aware of this Vaillant breakdown cover but they don't want you to know about it as they would much prefer that you deal directly with them so that they can charge you a small fortune for parts/labour repair. Had i not contacted Vaillant directly for a 2nd opinion , then I would have probably gone with the advice of the local heating company and replaced the boiler - so by contacting Vaillant I saved myself £1.5k.
Read more: https://www.diynot.com/diy/threads/f76-error-code-valliant-ecotechpro-boiler.118797/#ixzz56e74GnSh