Best Position for CH Pump

[Richard Radford]

I replaced the boiler last summer and took the opportunity to put in a 3 port valve to enable the hot water circuit to be pumped rather than gravity fed. I left the pump on the return rather than the flow side of the boiler. I suffered from pumping over and temporarily cured this by reducing pump speed. The problem I then had was that a couple of the TRV's went noisey. I replaced them but one has gone again after only a few months. Early morning startup: tap tap tap tap bl**dy tap. It drives me crackers.
I am about to fit a new bathroom suite and cylinder and want to take the opportunity to sort this out. I had intended re-plumbing the pump to be on the flow side of the boiler (adjacent to the boiler) and then into the 3 port valve. On the hot water side of the valve I propose to enter the cylinder primary at the bottom (apparently this helps convection heating) and on the output from the cylinder connect the vent and then the cold water feed (within 150mm of each other) before return to the boiler. There is little opportunity for me to put the cold feed/vent before the 3 port valve - to do so would require me pulling the house apart. Does this sound okay? Have I got the order right?

A second question: I want to take a feed from the primary to heat a towel rail in the adjacent bathroom, which should allow me hot towels in the summer when the heatings off. Is it okay to shunt the primary circuit like this?

 

[oilman]

To answer your first question, the order is not right.

The vent pipe (known as the open safety vent) should rise continuously from the boiler. It must be before anything else. This is a safety pipe and is IMPORTANT. This is beside the fact of being a building regulation requirement. You have a choice, you can either take your house apart and put the vent before the pump (if on the flow side) or before the 3 port valve, OR you can risk the heating system having a good try at taking the house down if a fault develops.

Some bits of building regs are arguably a bit daft, this ISN'T one of them.

 

[ChrisR]

What is the boiler - small chance there may be other options.

 

[bradleybear]

Firstly, it sounds as though your TRV's are fitted backwards (on the return instead of the flow pipes of the radiators), or if they are dual flow, then you haven't set them up right. The noise is what is known as water hammer, and happens when TRV's are fitted backwards.
Secondly, it is ok to tee into the primary flow from the boiler. You might want to fit a gate valve on the return of the cylinder to adjust the flow through the cylinder and rad, as it could starve other radiators of flow, it is called a balancing valve. Or fit a TRV to the bathroom rad to give zonal control in the bathroom, as it will get hot in there.

 

[bradleybear]

And finally, continued, your open vent and cold feed pipe want to be before the valve, otherwise there will be nowhere for system expansion. An aerjec, made by Myson are good, as they stop air being induced into the system via the F and E tank. You can pipe straight into these from the boiler flow, and to the valve. Just be careful, when you're valve shuts off, the cold feed and expansion will be isolated from the flow off the boiler.

 

[Richard Radford]

Thanks to all for the responses thus far, which have left me a bit confused and concerned in that the vent and cold feed were not directly connected to the boiler even before I started playing with the system. Is this a case of revised regs from when the house was built in the 70's?

Anyway, in terms of the piping layout I can get a cold feed and vent pipe down to the very floor of the house in the cavity that carries the soil stack. However, this means that the both pipes will have to go down to the floor and then back up a few feet to connect to the flow pipe from the boiler. Is this goig to be okay. Alternatively, I could just plumb the vent and cold feed directly into one of the two spare auxiliary ports on the boiler, which are close to the floor. Does this sound okay? This would leave the an arrangement of flow, pump, 3-way port, one circuit feeding heating circuit, the other feeding the hot water circuit.
Look forward to hearing from anyone who can help.

 

[Richard Radford]

Thanks to all who have offered help. I have purchased a Myson Aerjet, lots of copper tube and will be placing the whole lot BEFORE the 3-way port - best to do the job right!

 

[oilman]

However, this means that the both pipes will have to go down to the floor and then back up a few feet to connect to the flow pipe from the boiler. Is this goig to be okay. Alternatively, I could just plumb the vent and cold feed directly into one of the two spare auxiliary ports on the boiler, which are close to the floor. Does this sound okay?

No and no. You can have the feed and expansion pipe on the bottom of the boiler, but the vent pipe should come out of the top of the boiler. Cosmetics has to come second to safety.

 

[Richard Radford]

I'm with it now. Feed out of the top of the boiler, into Aerjet air separator from which run the vent and the cold feed pipes (appropriate ports and vent running directly up to F&E tank), then the 3-way port and off to the heating circuit and hot water cylinder both returning via separate return pipework until very close to the bottom of the boiler to avoid reverse circulation.
Once again appreciate everyone's assistance - I bought a book before starting this exercise and its helps but tends to assume a new installation. Whereas, I've inherited a gravity fed hot water system and non of the illustrations indicate the best way to convert such an animal.
Anyway, I'm doing it this weekend - I'll report on success or read obituaries if you hear nothing more!