Central Heating modification

DIYGriff · 4 Oct 2016

I wish to add a 3 port mid position valve to my open vented central heating system.

In the instructions I have read, it says that the boiler must have unrestricted access to the vent pipe.

Can someone please tell me if it is okay to install a new length of pipe Tee-ing off the supply pipe before the pump and tee-ing into the vent pipe above the cylinder supply. (i.e. red line on diagram) Could there be any unintended consquences of doing this.

Would it be acceptable to simply put a pipe around the pump and 3 port valve with a non return valve to stop any unwanted recirculation. (i.e. blue line) This would require a much shorter pipe run.

pipe.

Nozzle · 4 Oct 2016

The blue pipe and the red pipe do the same thing - and putting an NRV in the blue pipe would stop the re-circ flow but it would just go through the red one instead. Fluids flow from highest pressure to lowest. Highest being on the discharge, lowest being on the suction. Your red pipe links the two together, and that's where most of the flow will be.

DIYGriff · 4 Oct 2016

Would it be better then to cut the existing vent pipe next to the cylinder and join the red pipe straight into the vent pipe so that there is no circulation on that section of the system. Does the rest of the heating circuit between the pump and the return to the boiler need any venting for expansion?

Phill Peck · 4 Oct 2016

Where does your cold feed join the system?

DIYGriff · 4 Oct 2016

Phill Peck said:
Where does your cold feed join the system?

The cold feed is tee'd into the vent pipe next to the expansion tank.

Agile · 4 Oct 2016

The vent pipe should be connected immediately after the boiler and to nothing else!

An auto air vent should ideally be connected to the upper connection to the cylinder coil.

Tony

DP · 4 Oct 2016

Clearly in effort to pick on minor issue, main failing has been ignore i.e., the fed and expansion to header cistern is missing

Tony will I get a thank you for my enlightening post?

DIYGriff · 5 Oct 2016

Agile said:
The vent pipe should be connected immediately after the boiler and to nothing else!

An auto air vent should ideally be connected to the upper connection to the cylinder coil.

Tony

The current system is about 30 years old and was installed by a plumber so presumably it met building regs at the time. Is there any reason why the feed and expansion functions can't be met by the same pipe. Presumably once the system is full of water any expansion will rise above the inlet level from the header tank and over the spout back into the tank. If you make a small change to an existing system by adding a valve are you required to bring the whole system up to existing regulations.
I have altered the picture to show where the cold feeds into the system from the header tank.

I have seen diagrams showing a separate pipe running in parallel to the expansion pipe to supply the cold feed but I thought that since the pressures would be about even then one pipe could be used instead. As it is in the current installation.

DP · 5 Oct 2016

Griff, look at the diagram. How is the water from the cistern going to flow into the system?

DIYGriff · 5 Oct 2016

DP said:
Griff, look at the diagram. How is the water from the cistern going to flow into the system?

Sorry missed that bit from the picture have updated it now. The cold feed currently shares the vent pipe and tee's into it about level with where the supply pipe comes from the cistern.

DP · 5 Oct 2016

Lose the blue left of pump to valve or connect left of pump blue to new blue into header cistern
Red direct to vent pipe
Replace link that have between HW cylinder to header cistern with a vent plug
I would also fit a gate valve for balancing in the HW loop.

Agile · 5 Oct 2016

DP said:
I would also fit a gate valve for balancing in the HW loop.

I would fit a gate valve for balancing HW and CH too.

But somewhat surprised that you would since you like to put the full boiler power of 24 kW into the cylinder!

picasso · 5 Oct 2016

phod · 5 Oct 2016

You've got a combined vent and feed.
Do as in picasso's drawing above but without the blue line.
The red line is 22mm and should connect at the tank with combined vent and feed as in your own drawing.
HW Cylinder should be last Tee into the return before boiler.

DP · 5 Oct 2016

Agile said:
I would fit a gate valve for balancing HW and CH too.

But somewhat surprised that you would since you like to put the full boiler power of 24 kW into the cylinder!

Tony, you keep plugging 2kw for high power indirect coils and I will keep specing what the appliance manual demands
Perhaps I will take a leaf out of your book and start using 10mm copper pipe for gas lines for 30 plus kW boilers. Boiler will work but who needs all that power. If it takes a little longer, what is the issue? Not forgetting, condensing boiler will always be at full efficiency. It is a win win situation as pipe comes in a coil, so no pipe bending and no fittings needed. It even comes presleaved so that is another winner.

Perhaps you can enlighten me why the indirect cool is 22mm or larger bore if full power is not warranted.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Central Heating modification

Phill Peck

Similar threads