Gas central heating - open vented system design fault

[nairb999]

The system is 10 years old and always suffered air in the system - initially bleeding 1 radiator upstairs weekly and air would come out of the radiator for a couple of seconds. Over the years this has increased to several radiators - probably down to corrosion in the system. Now suffering kettling in the system above the pump. Put some sentinel x400 in the system and this has got rid of the kettling although I think must have some large deposits in the pipework above the pump as a magnet sticks to the pipework. An H diagram represents the piping arrangement. The 25mm pipe joining the 2 legs is 4" long. Top left leg 25mm air vent Bottom left leg 25mm from boiler Top right 15mm cold water and bottom right 25mm to pump. Sediment is in the middle leg plus the leg to the pump. Is this configuration OK. My next door neighbour has the same system as myself but the cold inlet is 2" to the left and they do not have any air problems. Could my design be the problem ?

 

[heatingman]

Remove the H arrangement and give a good clean out, also check the cold feed from tank is clear. Once happy that its clean replace it and ensure all joints are sound. Pay particular attention to the pump valve between pump and cold feed. Go up into attic and check that there is at least a 450mm dry vent pipe rising up over tank, if its just hooked over edge of tank it needs altering. Height of water in tank - top of vent pipe = dry vent length. Give the system a good chemical clean, remove rads and pump out in garden with hose if realy bad. Treat system with X100 and fit a good fitting lid to tank. A dirty system is not a quick fix!

 

[nairb999]

Many thanks for speedy response - dry vent pipe length is close to 1m and the lid is a good tight fit. Any other ideas why air could be getting in the system ?

Had the x400 in for 5 days - is it possible that if I leave it in for the max 4weeks that manufacturer states the remainder of the sludge might breakdown?

 

[heatingman]

The system could be creating gas due to chemical reaction, down to poor commission/install when new. Continue with thourgh chemical clean and treatment with inhibitors

 

[doitall]

Bamber Gasbag would tell you its wire wool in the system

 

[gas4you]

I've given up with X400 after a couple of jobs that didn't get cleaned too well by it. I now only use x800.

 

[nairb999]

X400 seems to be working as noises have gone. Just bled all radiators that had air problems and none emitted air. This is the firs time in 10 years. So all seems to be fine. All radiators at full heat.

How long should I leave it before flushing and adding x100 ?

Would you recommend that I still remove H section and clean before flushing ?

 

[heatingman]

I would remove & clean the H, X400 removes sludge deposits, x800 will remove the hard deposits from H. X800 is more aggressive and can should not be left in system. Whatever route you take the system must be thoroughly flushed out. Not a quick drain and refill.

 

[nairb999]

Thanks Heatingman - good advice.