Heating problem

[badwolf28]

I have an indirect heating system which was fitted about 15 yrs ago,the problem i have now is every time the heating is turned on the vent pipe in to the small tank in my loft runs full bore with hot water back in to the tank.any idears how i can stop this and why it is doing it would be very helpful.
thanks

[The Builder]

Usually, because either the boiler is turned up too high............or, more likely, boiler thermostat is faulty, and it's not shutting off properly.

[badwolf28]

Does the same thing if the boiler is on 1 and have fitted a new stat.

[The Builder]

I think we need a boiler engineer now ........... it really all depends on what system you have.
Do you have a "heat leak" rad? That's one that doesn't have a TRV (thermostatic rad valve)? If not, then there's nowhere for excess heat to go when none of the rads are "calling".
Just a thought.

[badwolf28]

yep have one of them as well lol

[badwolf28]

would a hole in the coil in the hot water cylinder make it over boil as well?

[terence7556]

a possible problem is pipework layout, which may not be the answer in this case as presumably the system worked ok before or a blockage in the pipework causing it to send the water up the vent pipework. do you have a cylinder in the airing cupboard? if so get one of your fridge magnets and see if the magnet will stick to the pipework that feeds off the F&E tank above in the loft, where it joins the pipework that tees from this feed ,the pump pipework and the c/h pipework.the magnet wont stick usually but if the pipe is sludged up with crap/hard scale then the magnet will stick.a quick test to try.
if it sticks then its a drain down, cut out the blocked pipwork and replace

[badwolf28]

no didnt work either thanks.pump works fine and is in the right way round and the 3 port valve seems to work ok as well but still vents over full bore when ever the heating is on,and the pump is only on 1 as well.