Hot water in header tank! Reassurance needed

[Vw1978]

Morning all, yesterday I changed a 3 port motorised valve on my sisters central heating as it wasn't working, once fitted and the system refilled I tested the valve and it works as it should, I thought all was ok until I went to put the ladders back in the loft and found red hot water coming from the vent pipe into the header tank, I immediately turn off the hot water and it stopped, the cylinder stat was set high so I turned it down to 60 degrees, I also turned the pump down from 3 to 1, the water level in the header tank is less than half full, I have had the heating and hot water both on individually and together and it no longer seems to be doing it, I am looking for some reassurance that this won't happen again, the only possible cause I can think of is that 2 days prior to fitting the motorised valve I moved a downstairs radiator and replaced it with a larger one which I drained the system down for, when refilling the system the ball cock in the header tank got jammed and the header tank was overflowing with the vent pipe submerged, not realising this straight away I had turned on the heating system, could this have caused it? It no longer has the vent pipe in the header tank as I have raised it.
basically I'm looking for possible causes and reassurance that it isn't going to happen while I'm not their.
thanks for any help you can give me.

 

[lame plumber]

get a qualified plumber to inspect your system and find the problem then sort it

 

[chris watkins]

If it is not doing it now, more than likely it was just an air lock that has now cleared, switch it back on & test / monitor it for a couple go hours tomorrow switching hot water & heating on/off & make sure it does not happen again.
P.S. keep pump on speed one & only turn it up to two if all the rads do not get hot, very unlikely you will need three.
& welcome to the forum BTW.

 

[Simon F]

welcome to the forum Vw1978
there are various possibilities as to what could be the issue.
possibly just a refill temporary issue.
you mention that you turned the pump down and the problem stopped, as a test turn the pump back up to see what happens. as said unlikely to need speed 3, how many radiators??
If it starts pumping over again then you could have a restriction between fill and vent pipes, you can test this with no level of certainty with a magnet.
who knows, all depends on how everything is piped up, position of pump etc.