Conventional Central Heating Mystery Pipe?

[Paul95]

Indeed, a deceptive photo.

It's a bypass but why you needing one on a Y-plan is unusual.

Do all your radiators have thermostatic radiator valves?

Not all, the hallway, utility, toilet don't, rest have.
Below i have added a diagram i found which shows a similar set up to mine, only one i could find showing this bypass pipe/valve.

Untitled

• Paul95
• 31 Jan 2014
• 1

 

[mogget]

I suspect it's there to maintain flow if the radiators are turned off, maybe someone more expert could comment?

 

[Blagard]

Right then for my next trick!

Does the 22mm pipe connecting near your pump go up to the bottom of the feed and expansion tank on its own?

Or does it vent over the top of it?

Or does it do both by branching off near the tank?

 

[gigz]

Seeing as you have a "Y" plan it can safely be closed as the flow will always have a path.

 

[Blagard]

Seeing as you have a "Y" plan it can safely be closed as the flow will always have a path.

+1

The example drawing the OP found is the S plan with two normally closed valves. As you say the Y plan always has at least one open port.

 

[Paul95]

Right then for my next trick!

Does the 22mm pipe connecting near your pump go up to the bottom of the feed and expansion tank on its own?

Or does it vent over the top of it?

Or does it do both by branching off near the tank?

It goes into the bottom of the expansion tank on its own

 

[Paul95]

Seeing as you have a "Y" plan it can safely be closed as the flow will always have a path.

thanks, i will close it tomorrow and see what happens.

 

[Blagard]

It goes into the bottom of the expansion tank on its own

As the pipe is coming off the flow, what you have there is a combined feed and expansion pipe in an arrangement that should only be used with the boiler manufacturers approval. So you need to check that, or post the boiler make and model and those who know it, and can advise.

Personally I would never do it that way even if the manufacturer says it is OK and I suspect that would be the view of most others here. As I have never come across one like that it needs some-one with wider experience than me to advise if that may be contributing to your problem.

 

[sooey]

Seeing as you have a "Y" plan it can safely be closed as the flow will always have a path.

+1

The example drawing the OP found is the S plan with two normally closed valves. As you say the Y plan always has at least one open port.

Not if it's all TRV's and they all shut.

 

[Blagard]

Not if it's all TRV's and they all shut.

You missed the bit where the OP tells us he has three rads not fitted with TRV's. So on this installation he can close the bypass for now.

However I would accept it would be much better to have an auto bypass where the gate valve is as it would only open if ever needed i.e. if some-one fitted the rest with TRV's and your condition occurred.

 

[gigz]

Edit

 

[Paul95]

It goes into the bottom of the expansion tank on its own

As the pipe is coming off the flow, what you have there is a combined feed and expansion pipe in an arrangement that should only be used with the boiler manufacturers approval. So you need to check that, or post the boiler make and model and those who know it, and can advise.

Personally I would never do it that way even if the manufacturer says it is OK and I suspect that would be the view of most others here. As I have never come across one like that it needs some-one with wider experience than me to advise if that may be contributing to your problem.

Thanks for all the help Blagard, thought when i originally asked the question regarding the bypass pipe it was a common item in CH systems. At least i think i know what it is for now.
I know i should start a new thread for my next question but seen as you probably know my system inside out by now i will through this one at you, hopefully this will be easy to answer.
Occassionally when the heatings been on for a few hours i get bad knocking for about 20 seconds, this seems to be on the single pipe coming down from the bottom of the combined feed & expaniosn tank and is then followed by the sound of gushing cold water back down the pipe, i suspect this has something to do with water from the CH system expanding into the tank then the CH filled back up again, is this right? and what could cause the knocking?

 

[Blagard]

The problem with that combined feed and vent is that when gas in the system is expelled via the combined pipe the space the gas took up has to be filled by water coming down the same pipe. So it would not be a surprise to have the pipe rattling around when that happens!

With a separate feed and vent the gas gets expelled at the vent and water comes back in down the feed - no conflict!

The close coupled arrangement of the connections you will see in many drawings like the example one you posted is to keep the pressures in the pipes as near as possible equal.

I would consider fitting a T to replace the elbow below the pump and loop a 15mm feed pipe from the bottom of the T to the connect with the bottom of the Feed and expansion tank. The current combined Feed and Vent I would cut in the loft and divert to vent over the tank. You would then have a better arrangement.

Just for certainty, can you confirm there is currently no vent pipe over the top of the feed and expansion tank.