no vent pipe in my CH system

[cutandbruised]

Hi All,

I've moved into a house where the CH is based on an old Thorn Apollo boiler and appears to be the standard wet system i.e. 2 pumped circuits one for HW and one for CH.

But there is no vent pipe, just a feed from a header tank into the system. There is air in the system and banging noises when CH is in use so I suspect this may be at least part of the problem. Is this lack of a vent pipe usual? Can the feed also act as a vent?

One possibility is that I install a vent pipe to try and sort the problem but where should it go? The boiler is downstairs and the pump and HW tank upstairs. I could easily put a vent pipe in the system as it enters/exits the HW tank. Easiest location is as the pipes leave the tank....I could just put a 'T' junction in at the 2port valve and vent the system up into the attic and across to the header tank.

Does this seem sensible and/or does anyone know of information regarding design of CH systems.

Thanks in advance,

Ian.

 

[ollski]

combined feed and vent should prevent air in the system must be 22mm though, try latching the valve open and bleed ing the air vents on the system pipework. It may be that the pump is pulling air into the system or it may be dirty and corroding.

 

[Paul Barker]

You need to make sure boiler isn't overheating. Such a system onl;y safe if there is a overheat stat fitted and working.

Check that from the boiler flow pipe which is minimum 22mm the first thing is a T which remains 22mm min and goes up to bottom of F/E tank other branch of T goes next to pump then on to both systems.

The first T is a negative pressure zone and it can be difficult for air to escape a negative pressure zone. If you change the T for a 28mm one the forced expansion at this point allows the air to escape up the combined feed and vent pipe. You could also try continuing up to the tank in 28mm, but that would not normally be necessary.

Alternatively fit an airjec at this point. In my experience the 28mm T works most of the time, but sometimes I fit an airjec, mostly for customers who have had a quote from British gas for £300 to fit one, so they know what they need but want a better price for fitting a £12 piece of copper.

Banging can be overheating also due to faults in boiler or sludge or scale. Make sure good means of air escape as above is in place, as Olski says encourage air to escape by manually opening valves but cutting power to system so that pump stops listen for glug glug, run system again, repeat often times.

Ger boiler stats checked out, make sure pump runs properly, cleanse system, descale until it's fixed.

 

[billybottle]

How do you power flush one of these then- especially blocking feed / overflow compared to normal system? Is there just the one hole to block (oo err missus! ) or is it not that simple? Cheers!