vent pipe problem

[pigfarmer]

i have recently built a large extension on my house, to all intents and purposes, it is a separate house, but both houses are using a shared ch/dhw system.

originally in my house, i had a firebird 90 oil fired boiler. the pump was on the return leg, right next to the boiler, and pushed the water into the boiler. on the flow side of the boiler, there was a 1 inch pipe( in ireland its all 1/2 3/4 or 1 inch pipe). this 1 inch pipe teed into 2 3/4 inch pipes. the pipe that was on the c/h circuit had a zone valve on it, and the pipe for the dhw didnt have a zone valve.

because the firebird 90 wasnt big enough, i bought a firebird 90/120 boiler. i installed it to the pipework on the original house and all was fine. i moved the cylinder, including the vent pipe that goes to above the small tank in the loft.

about a month later, i connected the pipework from the new house to the boiler. i connected a second cylinder and a second set of radiators to the boiler. i also installed a second vent pipe from the cylinder to above the small tank in the original loft. there are now 2 vent pipes above the smaal header tank.
when i installed this pipework, i didnt put in any zone valves, but a couple of days ago, i put in 2 zone valves, one for the radiators and one for the dhw. when i close both of these valves, (ie no ch or dhw on in new house) and i still have the boiler running for the original house, scalding water is being pumped out of the vent pipe from the new cylinder into the small header tank. however if i just turn the radiator system in the new house off, it stops flowing out of the vent pipe.

is there something else i can use instead of a vent pipe, so that the dhw system is sealed rather than vented.

any help would be greatly appreciated

cheers

simon

 

[Agile]

I will assume that the pump is powered by the boiler to provide an over run when the boiler shuts down.

Its normal now to have the pump on the flow but that should not make any difference.

I think the fault is that the feed pipe and the vent pipe are not connected correctly.

They should both be immediately after the boiler and with the vent connection first and the feed less than 150 mm ( thats 6" ! ) after it.

If thats correct there should be no pressure differential between the vent and the feed.

I find it difficult to believe that you can still buy copper pipe in inch sizes in Ireland rather than metric !

Tony

 

[doitall]

All sounds bl dy dangerous to me

 

[bripl]

from the ops description welcome to heating and plumbing in ireland the pipework sizes are different you get imperial sizes as well as metric plus one in the middle ,in most rural houses the pipework configurations would turn your hair grey overnight as for controls none just a simple switch wired to the pump and burner no stats gravity hot water is the norm sounds like you have a very wrong configuration consult a competant heating engineer/plumber

 

[pigfarmer]

to agile,

when you say the feed pipe, which pipe do you mean. if you mean the pipe that feeds the central heating loop, there is only one pipe and it is piped into the plumbing in the original house.

what i have essentially done is add 2 more zones to my existing heating system, one c/h zone and one dhw zone. there is only one header tank for the whole system, but the water that is being heated in the two cylinders comes from different storage tanks.

at the top of the new cylinder, the pipe comes out level using an elbow, then ive put a tee 3/4 - 1/2 - 3/4, with the vent pipe connected to the 1/2 inch branch. this is the highest point in the system, not including the header tank.

because the dhw loop in the original house has no zone valve, and has a vent, could i not just blank the vent on the second dhw loop because the first dhw loop will act as the safety.

one option is to have no zone valve on the second dhw loop and have it so that it heats both dhw loops whenever the boiler is fired up, but i really want to be able to have the new house independent.

cheers

simon

 

[Agile]

OK Simon, the "little tank" is the feed and expansion tank and has a small pipe from near the base going to your heating system. Thats the "feed" pipe!

The feed pipe MUST be connected just after the vent pipe is connected on the flow from the boiler.

Even in England, farmers have a reputation for holding everything together with string ( twine to farmers ! ).

When it comes to heating systems if you want it to work well there are a few things you must do for safety and correct operation! The feed and vent pipes are esssential for correct and safe operating.

Tony

 

[pigfarmer]

cheers for getting into this tony.

perhaps the name pigfarmer is a little misleading, i have no pigs and i am not a farmer!! and even tho i live in ireland, i moved here 3 years ago from england.

now thats out of the way, you say the feed and vent pipes should be 6 inches apart on the flow from the boiler, i have one feed pipe and 2 vent pipes, one on each cylinder. the vent pipe that is giving me trouble has no feed pipe on it at all.

why cant i treat the coil inside the second cylinder like a radiator, and not vent it at all. i know that i must find some way to 'bleed' it

cheers

simon

 

[Agile]

Now we know that you are not a pig or a farmer and only have two vent pipes we might be getting somewhere.

You should have THREE vent pipes!

One on each cylinder on the hot water outlet and these should terminate ( end ) above the cold water tanks.

You should also have a vent pipe as I explained for the heating !

Please dont lose words as that could cause you difficulties! The heating feed pipe should be at a MAXIMUM of 150 mm ( 6" ) after the vent pipe. It should be less than 150 mm if possible.

Tony

 

[pigfarmer]

ok tony we could be getting somewhere here. in total i have 4 vent pipes, one from each cylinder h/w output going to the main storage tanks ( one in each house) and i have 2 vents for the heating system, one as described, near the feed pipe on the original cylinder and one on the new cylinder which has no feed pipe. both of these vents go to above the header tank. can i delete one of these vents, and if i can which one should i delete? the two cylinders are in the same room, the new one is higher than the old one. the lower cylinder has the feed pipe connected to it.

also on a different note, which pipe from the boiler goes to which connector on the coil in the cylinder

cheers

simon

 

[Nige F]

Any advance on 4 Far Canal