Excess coolant from header tank

[Ginger Teddy]

Hi folks, I hope somebody can help with this issue, I parked the car( 2004 1.8t) with offside on the pavement in order to wash it ( two days ago) and let the car idle while I did this. During this time the fan cut in on slow speed ( nothing unusual about that ) for approx 60 seconds and then shut off and I carried on and roughly 10minutes later the fan ( on slow speed) cut in again and a couple of minutes later it went on fast speed . It had sat idiling for 20minutes since I had started so I wasn`t unduly worried, it had now been on fast speed for around two minutes when I parked it back on the drive.Temp gauge remained at 9 o`clock position. I switched engine off and the fan on fast speed continued for possibly another minute then it shut off.I went to the car today and went to do the usual coolant checks etc ( always do coolant check before any journey ) and on starting to turn cap , coolant came out over header tank and area, I didn`t open cap any further and tightened it up again( while I rinsed coolant from the area). I attempted to open cap again and same occurred so tightened it up once again.I tried one more time to remove cap and coolant again came over the top of the header tank and I continued to remove cap completely and coolant was up to the top of header tank.(engine was now of course stone cold).Headgasket replaced in April 2018, done 3k since then, no mayo on oil cap.Any advice appreciated regards Paul