HW in CH Header (probably yet again!!)

[66BaldEagle]

Hi, Fairly new to forums. Look for previous posts without success.
I have a Potterton 50e Boiler Honeywell ST7100 Programmer, Sundial Y plan.
The system has been running well for years, nothing has been replaced in the last year (room stat changed about 1 year ago, pump about 3 years ago, along with 3 port valve, cylinder and cyl. stat)
Recently hot water is travelling up the cold feed from the ch header tank, filling the tank and overflowing, this 15mm pipe is adjacent to the 22mm vent pipe which also gets hot all the way up but appears dry on the end of the vent. Fernox was in the system 3 years old probably shot to bits by now,
Have had problems with ignition cycling on off without firing-dry joints arcing in control unit.
Is this all down to boiler stat(which doesn't seem to turn boiler off even in off position) I ask as it doesn't take long for water to start flowing into tank-rads aren't even fully hot
It makes no difference whether program is set to HW or CH
Hope you can help. Mike
I still have Installation & servicing Instruction Handbook for 50e if anyone needs a copy (PDF)

 

[bengasman]

Could be a busted cylinder

 

[snakeio]

sounds like ur cold feed is blocked on ur ch feed tank.

ur boiler will be overheating- and albeit its making a nice loud banging noise as well!?

 

[david17uk]

I'd say the cold feed may be blocked too...

Try turning the water supply to the tank off (or tie up the float valve) Then drain the radiators. Turn the tank back on and see if your rads fill back up.

Now's a good time to add some cleaner then inhibitor to your system

 

[seco services]

if you say the boiler stat isn't working is it not tripping the boiler out and needing resetting all the time ?

 

[66BaldEagle]

Thanks for responding guys,
I had an inkling that maybe the cold feed was being blocked (gathered from previous similar posts) but with the amount of water that has gone out the overflow it has to be coming from somewhere ( the rads aren't full of air) as it happens with CH I sort of discounted the leaking coil in the cylinder.

Will be using mains pressure to backflush the system this weekend, will check if rads fill back up
By the way the boiler doesn't bang it seems to run fine, once the tank fills up and runs out the overflow I shut the programmer down, the overheat doesn't trip.

I have just bought on eBay a new electronic controller, overheat heat switch and paste. Locally I have ordered for tomorrow a new thermostst and shiney new knob.
What do you guys reckon is the best stuff to flush the system with?

 

[seco services]

won't be the cold feed blocked as you say its coming up the cold feed not the vent pipe.

have you tried isolating the cylinder to check its not the coil ?

 

[66BaldEagle]

Assumed it wasn't coil as it happens when CH only is on (and with HW)

 

[seco services]

can still be coil.
is the cws filling at the same time as the f/e ?

 

[66BaldEagle]

No the cws doesn't fill up at the same time.

 

[seco services]

sounds like a blockage somewhere then.
use either sentinel x800 or x400.
if its a solid block it may need the pipe cutting out and replaced.