Air in (indirect) system

[mchandler]

I understand that the cold feed should drop in behind the pump, and within six inches of the open vent. A friend's system has the cold feed connecting directly into the vent pipe - it's just a t-connection, and not an air release/vent chamber. Will this cause air problems in the system?

There is an added problem - the return from the domestic hot water heating coil is 10mm, and 15mm going in. I'm going to change this to a 15mm anyway.

The system is particularly noisy on changeover (from hot water only to heating) and therefore is worst this time of year as the heating is starting to be used. Any advice welcome. thanks.

 

[diesel_ltd]

a combined cold feed and vent is very common and not a good job at all i was suggest you repipe it when your doing the coil i would always do the coil in 22 and balance it down with a balancing valve.
is there any controls on the system ie cylinder stat, room stat, auto by-pass??
As for the noise is this due to air in the system??

 

[mchandler]

Diesel, thanks.
Yes there is a room stat - not sure about anything else I'd have to look again.
I'm learning so please bear with me - you mentioned balance valve? Would you suggest I repipe this flow AND return of the heating coil in 22 ? It does come off the main run and return in 22 but for some reason the flow intot the couil is reduced to 15 and the return reduced to 10! I'm told this system is officially a 'bodge job' and I was hoping to help solve th air problem which I suspected came from
a) the 10mm return from the coil going into a 22 return to the boiler?
b) the cold feed connecting directly to the vent?

My own system has a vent chamber/ air valve where the cold feed connects with the vent pipe. Is it important that both are separate if there is no vent chamber?
thanks again

 

[diesel_ltd]

yes i would pipe the coil in 22mm and you can use a 22mm lock shield valve (looks like a gate valve with no head) to balance the flow of water to the coil, this is so that all your heat doesn't go to the coil when you have heating and hot water on.
it is important to have your vent and cold feed seperate this let the air vent up the vent and when your cold feed is tee'd in with 6 inches it stops your system from drawing air down the vent due to the the water in your f&e tank pressing down.
The vent pipe should aways bee the first tee off the flow coming from the boiler followed by the cold feed and then your pump.
check and see what controls your friend has on this system, room stat cylinder stat, motorized valves (1 or 2) auto by-pass valve or thermostatic rad valves cus there might be other causes for the noise

 

[mchandler]

Diesel, you've given me plenty to go with there. Many thanks.

 

[diesel_ltd]

ps your balancing valve goes on the return from the coil

 

[crashndie]

if the system has been combined cold feed and vent at some point, it may mean the system has been pumping over or dragging air in it may b worth doing a full combined cold feed and vent to pervent any problems you may have after you fill up. the cold feed should be in 22mm all the way to the tank swap the 15 mm cold feed out let for a 22mm one and still do the vent over the tank. i do this on all my new system or boiler swaps the system cant drag air in or pump over but can expand as req