OK, bear with me please, Golf 2013 mk 7 2.0 diesel 115K, owned the car for 8 years I had a full service when I bought it at approx 45K, then all I've done since is an annual oil/filter change and a cambelt a few years back and then rear discs/pads last year. Otherwise no other repairs/maintenance! 
I have noticed the car has maybe taken slightly longer to start first thing in the mornings over perhaps the last 6 months but very subtle if so. Over the last say three weeks the car has (every few days or so) had a sudden loss of power for a split second as if you'd hit the brakes, then behaves as normal, very subtle/quick, Mrs Mercury didn't even notice.
Fast forward to today whilst driving and a flashing glow plug lamp along with an 'error start-stop system' message and a lack in power, hardly anything when you put your foot down, unfortunately I was about 40miles from home all via dual carriageway and on long or steep ascents I had it in 4th gear with the foot on the floor and it would not go above about 55mph even with a good (90mph) run up.
Anyway got home, turned engine off, let the whole thing switch off and restarted the engine, it sounded like an absolute bag of spanners and really struggled to start but it did start, then there was a consistent glow plug lamp & Emission control/Engine management lamp displayed + the 'error start-stop system' message. I though I'd repeat the process and take a video which I did, exactly the same results - bag of spanners/just about started, both lamps on. Except somehow I buggered up the video so I went on to repeat the whole process ...
But this time when I turned the ignition it restarted instantly with no weird sounds and only the Emission control/Engine management lamp displayed. So took it for a test drive and it drove just fine apart from the lamp.
I arrived home and repeated the whole process, ignition off and car 'reset' as if I'd locked I down and got back in, re-started the engine and this time started just fine, no sounds, and no warning lights at all - the car is now seemingly fixed, an early Christmas Miracle perhaps or some annoying intermittent fault that will cost me more than my next years annual utility bill?
My understanding is that the glow plug lamp flashing is actually reporting 'fault in the engine management system' rather than anything to do with the glow plugs, which presumably would only affect the starting anyway.
I don't have anything to check the errors (if present), should I bother? Any thoughts or obvious/easy things to change or other insights? It's a while since I fixed my own cars but could probably do some simple stuff, otherwise book it into my local garage, VW specialist or I do have a Bosch garage not so far away? My plan at the moment is to just drive it as normal (avoiding motorways etc) and book it in to my local garage which I expect will be next week unless it fails in the meantime.
I have noticed the car has maybe taken slightly longer to start first thing in the mornings over perhaps the last 6 months but very subtle if so. Over the last say three weeks the car has (every few days or so) had a sudden loss of power for a split second as if you'd hit the brakes, then behaves as normal, very subtle/quick, Mrs Mercury didn't even notice.
Fast forward to today whilst driving and a flashing glow plug lamp along with an 'error start-stop system' message and a lack in power, hardly anything when you put your foot down, unfortunately I was about 40miles from home all via dual carriageway and on long or steep ascents I had it in 4th gear with the foot on the floor and it would not go above about 55mph even with a good (90mph) run up.
Anyway got home, turned engine off, let the whole thing switch off and restarted the engine, it sounded like an absolute bag of spanners and really struggled to start but it did start, then there was a consistent glow plug lamp & Emission control/Engine management lamp displayed + the 'error start-stop system' message. I though I'd repeat the process and take a video which I did, exactly the same results - bag of spanners/just about started, both lamps on. Except somehow I buggered up the video so I went on to repeat the whole process ...
But this time when I turned the ignition it restarted instantly with no weird sounds and only the Emission control/Engine management lamp displayed. So took it for a test drive and it drove just fine apart from the lamp.
I arrived home and repeated the whole process, ignition off and car 'reset' as if I'd locked I down and got back in, re-started the engine and this time started just fine, no sounds, and no warning lights at all - the car is now seemingly fixed, an early Christmas Miracle perhaps or some annoying intermittent fault that will cost me more than my next years annual utility bill?
My understanding is that the glow plug lamp flashing is actually reporting 'fault in the engine management system' rather than anything to do with the glow plugs, which presumably would only affect the starting anyway.
I don't have anything to check the errors (if present), should I bother? Any thoughts or obvious/easy things to change or other insights? It's a while since I fixed my own cars but could probably do some simple stuff, otherwise book it into my local garage, VW specialist or I do have a Bosch garage not so far away? My plan at the moment is to just drive it as normal (avoiding motorways etc) and book it in to my local garage which I expect will be next week unless it fails in the meantime.
I'll dig my (unopened 
) Haynes manual out, I noticed on the Haynes YouTube fuel filter change video they removed and discarded all of the leftover fuel in the filter housing, is that strictly necessary? Guess it matters not as I'll need to get (one of those red fuel tanks) with some spare fuel to top up the new filter in anycase.