One Pipe C/H System Issue - Rads Cold

[SniperOne]

Changed 6 rads on a one pipe c/h system today, and you've guessed it one part of the house gets hot and the other stays cold.

I think that the water is taking the shortest route and despite shutting off all the rads that were getting hot it still will not flow the way i want it too?

The flow pipe leaves the boiler and goes into the roof space, there is a T piece that diverts the water to the front and rear of the house.

The hot water is flowing to the front of the house only and returning back to the boiler without flowing to the rear of the house, so the boiler is cutting out as the water temp is too hot.

I have left the house tonight to allow the water to cool down and then will try again in the morning, just hoping that there is know air left in the flow pipe to the rear of the house and that tomorrow it will heat up and then i can open up the rads at the front of the house again.

If this doesent work in the morning, what else can i try?

Can i put a gate valve in the flow pipe towards the front of the house and have that shut off whilst trying to get the hot water flowing towards the back of the house and once we are up and running, slowly release the gate valve to allow the water to flow towards the front again?

Hope it all makes sense lol

 

[Boilerman2]

Turning off Radiators will not change the circulation around the 1 pipe loop
however usually there are lockshield valves located in the Returns near to where they join up at the return to the boiler these are the valves that can be adjusted to balance the flow between the front & Rear circuits the circulating pump (if there is one) is normally on the Return on this type of system

 

[SniperOne]

PS

The boiler is a Vaillant Combi if that makes any difference, it's not a gravity sysytem.

 

[doitall]

Did you fit TRV's when you changed the rads and what make/model.

How are the rads connected TBOE or BBOE.

Circuit balancing valves have already been mentioned.

 

[SniperOne]

Customer wanted us to use the old Honeywell TRV's that were on the old rads, every rad has one.

The last time the house had some rads changed was 8yrs ago and the Plumbers back then had some issues aswell, apparantley.

The only LS valves are on the rads, please explain what you mean about cirulating valves or valves near where the return goes back into the boiler?

Rads are connected BBOE if that means at the bottom on both ends?

 

[doitall]

What you have is an old gravity circuit that's been converted.

Is there a means of drawing the air from both circuits after the split.

At the high level where they split there should be a lockshield valve and air vent on both flows so you can get the air from both circuits.

There should also be lockshield valves where the two returns become common so you can balance them.

 

[SniperOne]

No, there are no LS valves on flow pipes and can only draw the air on the rear circut (flow and return) via the air vents at high level, there are no air vents on the front circut that i have seen.

Not seen any LS valves near the common return either.

The problem is on the rear circut but that's where i have air vents?

 

[doitall]

If you have a common air vent it can take the air from one circuit and leave the other locked.

A back feed with a hose pipe may do the trick if your careful.

 

[SniperOne]

I am wondering how the plumber 8yrs ago managed to get it to work, it obvioulsy does but it's frustrating finding the way.

 

[SniperOne]

If you have a common air vent it can take the air from one circuit and leave the other locked.

A back feed with a hose pipe may do the trick if your careful.

there is not a common air vent.

how do you back feed a combi?

 

[Boilerman2]

Sounds like a C++K up with a Capital K!!
Surely you looked at the job before taking it on????
You have a Combi so i assume that the system has been Sealed>>
where the Open vents were taken of the cirulation pipe work (there could be more than one!) there should now be a good quality AAV such as a spirovent?? there may be venting points that you have not yet found!!

 

[Blagard]

What you have is an old gravity circuit that's been converted.

That is quite possible, in which case there may be a check valve on one of the circuits causing an airlock. If you find one, you may be lucky if it has a built in vent point. (During an earlier conversion, it could be they left hot water on gravity and pumped the C/H hence the need to put in check valves).

 

[doitall]

Need to able to turn the one loop off so as to vent the other loop.

Or you need to drain the lot out and fill from the bottom.

 

[SniperOne]

Yes it is rather annoying!!

Assumption was that it was standard two pipe system (could see flow and return pipework on some of the rads) and not till we lifted the floorboards in a bedroom to move some pipework for the last rad did we notice that there was a one pipe system present.

I believe that the front of the bungalow is a one pipe arrangement and the rear is on a standard flow and return arrangement, the 3 rads that don't get hot are on the standard flow and return setup.

The combi and some rads were changed 8yrs ago, the owners had the same issue back then once the rad and boiler work had been done.

 

[doitall]

Almost certainly an air lock in the return pipe. you could turn all the flow valves off and see whether you can pull water through the return pipe.