CH Question

[cr0ft]

Hi all,

We are currently renovating an old property in the centre of Lincoln. The owner is adamant they don't want to replace the existing floor standing boiler as long as it's safe. We are replacing the existing indirect vented hot water cylinder with a larger one of the same type. There is currently an open vent on the hot water system in 15mm so we will be upgrading that to 22mm. There is no open vent on the CH system so we will be running one off the primary coil return. There is a cold feed in 15mm to the system obviously but this goes into the wall and we're not sure where it tees into the system. Does anyone have any ideas where it's likely to tee in as I would like to connect it in on the primary coil flow in preparation for converting the system over to a fully pumped S plan system. Only ever seen cold feed pipes connecting into the coil flow in the airing cupboard before and don't want to take the house apart to find it really!

 

[Ermintrude]

You checked on boiler. Not unusual for cold feed and vent to be on boiler?

 

[cr0ft]

I am popping over tomorrow PM. It's an older floor standing one. Gravity 28mm hot water at present and 22mm CH flow/return. There is no open vent running back over the feed/expansion tank at present but the cold feed may well be running down to the boiler, will check tomorrow. Did older boilers just use the cold feed to vent up if required then? Never seen a CH system without an open vent before.

 

[chris watkins]

cr0ft it is not a cold feed, if the system has a primatic cylinder it is filled & vented via that.

 

[cr0ft]

I'm not 100% convinced it was a primatic. The apprentice pulled it out and he said there was a coil running up and down the middle of the cylinder - I think it was just an older design of indirect cylinder to be honest. The hot water side of the cylinder is as I would expect it to be plumbed in now except that the open vent is in 15mm. That's easy sorted though.

There is a cold feed pipe running down from the F/E cistern which definitely doesn't run into the old cylinder, it goes off into the wall then presumably downstairs. I will check behind the boiler tomorrow.

Yeah, ignore my first post. Definitely not primatic as the cylinder was fed from the CWSC as normal and the heating is definitely fed from the F/E cistern.

 

[Nostrum]

Cold feed on cylinder flow with an s plan is a recipe for disaster!

You'll need to get both the feed and vent in behind the pump, wherever that will be.

if it's primatic the cold feed and vent for heating will be in the cylinder!

 

[Chalked]

You answered your own question in the post.

its a primatic cylinder. To convert to indirect ,You will need a separate storage cistern and run a vent from the gravity flow and a new cold feed into the return.

 

[Chalked]

I'm not 100% convinced it was a primatic. The apprentice pulled it out and he said there was a coil running up and down the middle of the cylinder - I think it was just an older design of indirect cylinder to be honest. The hot water side of the cylinder is as I would expect it to be plumbed in now except that the open vent is in 15mm. That's easy sorted though.

There is a cold feed pipe running down from the F/E cistern which definitely doesn't run into the old cylinder, it goes off into the wall then presumably downstairs. I will check behind the boiler tomorrow.

Yeah, ignore my first post. Definitely not primatic as the cylinder was fed from the CWSC as normal and the heating is definitely fed from the F/E cistern.

One dimple way yo check.....
how many tanks in the loft ? If it's one, it's primatic.

 

[chris watkins]

If there is an F&E, it's not a primatic system (unless it has been extended on the heat over the years)

 

[cr0ft]

Sorry for the confusion. Looking at that diagram it definitely isn't a primatic cylinder (the apprentice has done all the stripping out and removed it whilst I was not there, I think he got confused looking inside it, I didn't get a chance to see the old one really). There are the usual 2 tanks. I've never come across a primatic cylinder in over 6 years of trading tbh.

@Nostrum, not meaning to doubt but why is cold feed on cylinder flow bad news? I know it's not the best way to do it but if we are converting the system to S Plan the pump is in the boiler so we can't really do much re positioning so this is the best we can do I think? The pumped water on the hot water circuit is going to take the route of least resistance which is always going to be through the 28mm coil as opposed to up the 15mm pipe against gravity. I can't really do much with the position of the pump as it's inside the boilier that's why I'm asking.

 

[cr0ft]

Just checked this out and learnt something new (I don't do a lot of heating work really). Now understand why it's best to run the CF, open vent (within 6") and then the pump. Will take a closer look at it tomorrow!

 

[Chalked]

Better to fit an air separator if your going with open vent.
Pic is sideways,vent off the top.

 

[Ermintrude]

See lots up here and elson tanks. Boosh !

 

[Reg Man]

F&E cistern means it is not primatic. They have put a 15mm pipe in to act as combined cold feed and vent, illegal. Must be 22mm if mi's allow it. I would look at reconfiguring the set up to standard H, vent and cold feed on primary flow just before the circulating pump. Upgrade it so that next year when the floor standing boiler fails, you don't have a dogs diner to convert it to an efficient wall mounted boiler.

 

[cr0ft]

Heyup all. Ok here is the deal! Looked at the job myself today in more detail. The old cylinder was an indirect vented cylinder but with no open vent to the feed/expansion cistern lol. Obviously we've fitted one today on the new cylinder, that bit is easy.

The current setup is a combined cold feed and open vent run in 22mm (not 15mm) from the F/E cistern which tees into the current gravity flow to the primary coil. CH is pumped and the circulating pump is inside the boiler itself. I am planning on using the existing combined cold feed/open vent as the new cold feed and leaving it as it is. I'm going to run a 22mm open vent pipe off the top of the primary coil gravity return. I will then be converting the system to S-Plan. There is no way to connect both in behind the pump given the current setup.

The motorised valves etc will go by the boiler in a new cupboard to be built in the kitchen.

 

[Chalked]

That will pump over like a good un!
vent will need to go before the pump.

 

[stevetheplumber]

how can you put a s plan on gravity ?if the pump is in the boiler i would assume its on the heating return

 

[cr0ft]

@Stevetheplumber - Not sure what you mean tbh. You just cap off the gravity hot water side of the boiler then connect the hot water gravity flow and return to the central heating flow and return using a motorised valve on the flow. Just like any other s-plan system except the hot water pipework is in 28mm.

@Chalked - I've had to do this setup with cold feed and open vent before. Where I've done it before the pump doesn't pump back up into the tank where the cold feed is on hot water flow. There is a bloody great big coil in 28mm it would prefer to run round. Water always follows the path of least resistance and all that. The reason I know it works this way is we put open vent on the flow the first time round by mistake and the water did indeed pump over 🙂 Switching the open vent and cold feed round sorted the issue a treat.

I'm happy enough with it now I've worked out how they've done the system. I do agree it's not an ideal setup, but if you saw this house you would agree that it's not possible to get them into the ideal position behind the pump.

 

[stevetheplumber]

sorry i thought you were leaving gravity circuit in

 

[solutions]

@Stevetheplumber - Not sure what you mean tbh. You just cap off the gravity hot water side of the boiler then connect the hot water gravity flow and return to the central heating flow and return using a motorised valve on the flow. Just like any other s-plan system except the hot water pipework is in 28mm.

@Chalked - I've had to do this setup with cold feed and open vent before. Where I've done it before the pump doesn't pump back up into the tank where the cold feed is on hot water flow. There is a bloody great big coil in 28mm it would prefer to run round. Water always follows the path of least resistance and all that. The reason I know it works this way is we put open vent on the flow the first time round by mistake and the water did indeed pump over 🙂 Switching the open vent and cold feed round sorted the issue a treat.

I'm happy enough with it now I've worked out how they've done the system. I do agree it's not an ideal setup, but if you saw this house you would agree that it's not possible to get them into the ideal position behind the pump.

Could you not bridge the pump valves in the boiler and relocate the pump to the cylinder location use the Old 28's as primaries from boiler to pump zone valves by cylinder and link in to rad circuit at closest point. Then you could have your standard feed and vent H at the circuit neutral point.
Then again if what you have done works..... more power to ya.

 

[Nostrum]

Or take a tee off the existing pumped flow from boiler to the cylinder with m.v,s for s plan. Use 1 existing 28mm for the cylinder return, and the other as a combined feed and vent straight back to boiler.

 

[solutions]

Or take a tee off the existing pumped flow from boiler to the cylinder with m.v,s for s plan. Use 1 existing 28mm for the cylinder return, and the other as a combined feed and vent straight back to boiler.

Nice thinking there Nostrum. Off site pipe route visualisation, some cant do that when they are staring at the actual pipes.