Water running into the header tank

[Fly100]

I have a y plan system.when the water is on and the heating I get water cycling up the expansion pipe back into the header tank.
All the rads run free as does the hot water system and the motorised valves all appear to have full movment....

Any ideas anyone
thanx
FLY

 

[keego]

What speeds the pump set on? if it's on 3 try putting it on 2 & see if the pumping over stops.

 

[Fly100]

its on number two...if i drop it to nmber one the heating strggles to heat all the rads

 

[Paul Barker]

A number of fixes.

Increase volume of feed expansion pipe so it is a greater proportion of system volume, I think it's meant to be 8% or something.

Raise hight of tank and also of open vent above it.

If all else fails put feed expansion pipe into open vent.

Does pipework go Flow from boiler, T for open vent, very close to that T for feed expansion (which preferably goes in from underneath), pump? Helps with air removal if first T is one size bigger than required. Or better still if AIJEC used instead.

If all above correct and you cannot get sufficient hight for fe tank and open vent to not pump over then consider converting to a semi sealed system where you don't have an open vent, just a feed expansion pipe in 22mm. Boiler must have an overheat stat and best to fit a PRV though you'd have to get a hell of a block in your feed expansion pipe before the prv kicked in. FE tank then becomes an expansion vessel working at atmospheric pressure. Check with boiler manufacturer first. Servowarm were doing this for years, don't know what they're up to now. They were allowed to do it because of the extra controls in their boilers. Most modern boilers have same controls these days. You must check with manufacturer first though.