Expansion Continually flowing

[SquiddlyDiddly]

Hi,

I have a gravity hot water and pumped central heating system with a conventional condensing boiler. I have an S plan set-up with 2 port valves.

I noticed that when the central heating is being pumped, water continually flows out of the expansion pipe into the expansion tank.

I need to know how to stop this happening.

May I add, that I do not have a cyclinder thermostat at the moment and the expansion pipe comes off the central heating return near the hot water tank which is sited in the loft.

Thanks for your help.

 

[45yearsagasman]

You do not have gravity hot water on a condensing boiler, or at least you shouldn't have. You have a fully pumped system and it does sound like the cold feed and expansion pipes are connected at the wrong place into your system. This is a general rule of system configuration that will work. View media item 32248Note where the feed and vent pipes are connected. If yours are not like this then then it needs correcting.
Pumping over will cause rapid damage to your system.
Why is there no cyl stat and how do you limit the temp of your domestic hot water, and where did your installer tie his horse.

 

[SquiddlyDiddly]

The diagram accurately depicts my system.

I don't have a cylinder thermostat as one has never been fitted. I do plan to add this to reduce the hot water temperature.

The system has been in the house ever since we moved in 20+ years ago. Two years agao I replaced the boiler, pump, 2 port valves and programmer but the pipework is donkeys years old.

I am still unclear about the feed and expansion to the central heating.

For convenience it seems, the expansion tank feeds the central heating in the loft and the expansion pipe as vitually alonside it conecting to the central heating.

I was hoping to be able to do something without having to disrupt too much of the house with extended pipe runs. Do I need to make the feed and expansion entry into and exit from the central heating down near the boiler rather than up near the hot water tank.

I know it must be frustrating with someone of your experience dealing with an amateur. We have been let down badly by tradesmen before and so I like to research what needs to be done so that we do not have the wool pulled over our eyes when we get the man in.

Andy

 

[45yearsagasman]

The feed and exp connections should be on the flow from the boiler and just prior to the pump (on the suction side). If this rule is adhered to and you still get pumping over then you must look for restrictions in and around these connections and also the height of the exp tank above the system together with the height of the vent pipe above that tank. This is all relevant and ignoring these rules will give problems. Some pics of the system connections would help.
No frustration felt and pleased to help.

 

[Dan Robinson]

If the digram accurately depicts you system, then you do not have gravity hot water circulation. You said yourself you have an S-plan. Which also means you should have a cylinder stat to control the hot water zone valve.

What make and model boiler is it?

A cheaters way around this would be to combine the feed and vents.

 

[45yearsagasman]

Quote:-A cheaters way around this would be to combine the feed and vents.

You mean like this Dan:- View media item 29821

 

[Dan Robinson]

Summut like that - but of course only if the boiler MI's say you can do it.

I still the OP has mus-identified the layout of the system somewhat....

Anyway - time to drill a whole in my floor...

 

[spareshunter]

SD. If the diagram is as shown then 1: empty expansion tank and get water level down to 2 inches (which is where it should be on all systems especially flats with low head available)above feed pipe, adjust float valve to suit fill. 2: Turn pump to lowest functionable speed. If that fails extend expansion pipe as high as it will go or at least 2 foot but you will have to experiment with that.

First two options cheap as chips.

 

[SquiddlyDiddly]

Yes Yes Yes I did misinform you about the gravity hot water system - Sorry.

Thank you for your suggestions etc.

spareshunter, I didn't think of turning the pump flow down and that might help but I think I am going to have to move the feed and expansion pipes so they connect as per the info supplied by 45yearsagasman. Didn't want the disruption to floors / walls / plaster / whatever but it seems I will have to bite the bullet and have it done

Just for information as I don't know how to post photos to the forum........

The header tank is at the highest part of the apex of the roof and has about a 3 foot drop to where it is connected to the cebtral heating pipe. The expansion pipe comes off the same part of the central heating circuit just before it goes through the cylinder and loops up and over the header tank.

Hope I make sense - but probably not.

 

[matt1e]

The system has been in the house ever since we moved in 20+ years ago. Two years agao I replaced the boiler, pump, 2 port valves and programmer but the pipework is donkeys years old.

from the above post it seems that you have a heat only boiler,where is the pump situated in the system? my money is on the return

The header tank is at the highest part of the apex of the roof and has about a 3 foot drop to where it is connected to the cebtral heating pipe. The expansion pipe comes off the same part of the central heating circuit just before it goes through the cylinder[b/] and loops up and over the header tank.

Hope I make sense - but probably not.

are the pump and valves after this connection?

Matt

 

[SquiddlyDiddly]

Mattie I am not sure of the position of the pump. All I know is that the installer said he was doing an S plan. BUt I do not know whether he really knew what he was doing. He was recommended but when he came I established he was not gas registered or electric registered. So he had to call in a Gas Safe man to connect the gas and an electrician to do the electric. He didn't seem to know what he was doing either and was on the phone to someone whilst connecting up the electrics.

So I am not sure how I identify flow and return unless the installer wrote it on the pipes. I will have a look when I can.

 

[Space cat]

First off, try to avoid the word "expansion" because it's easily misinterpreted. In fact you've done it yourself. You have a feed pipe coming out of the header tank and a vent pipe hanging over the top. Expansion takes place up the feed pipe.

Do I need to make the feed and expansion entry into and exit from the central heating down near the boiler rather than up near the hot water tank.

No! There MUST be an unbroken, upward path from the top of the boiler's heat exchanger all the way to the open end of the vent (except for the final bend of course). A vent pipe is normally connected high up in the system. Any pipework above this will need a bleed valve on it.

When the pump starts, the point at which the feed pipe connects is the one point in the circuit where the pressure doesn't change. At all points upstream, all the way to the pump, the pressure will go up (unless you have pipes of different sizes in the circuit, for which see below). Connect your vent too far upstream and this pressure increase will cause the problem you have. The two pipes should connect as near to each other as possible and, ideally, the vent should be downstream of the feed.

The other thing you have to watch out for is the venturi effect. This happens if you have different sized pipes in the circuit. It might be counter-intuitive but, when the water starts moving, the pressure will be higher in the larger pipes.

If your pipe layout is all wrong, one way out is to disconnect the feed pipe and tee it into the vent pipe close to where the vent pipe joins the circuit. You can incorporate a small U-bend into the feed pipe if you like to make sure air can only go up the vent.

 

[matt1e]

Mattie I am not sure of the position of the pump.

do you mean you dont know where it is in regards of the system pipework or you dont know where it is at all?
what is the make and model of your boiler?

All I know is that the installer said he was doing an S plan.
BUt I do not know whether he really knew what he was doing. He was recommended but when he came I established he was not gas registered or electric registered. So he had to call in a Gas Safe man to connect the gas and an electrician to do the electric. He didn't seem to know what he was doing either and was on the phone to someone whilst connecting up the electrics.

they didn't, and to miss out on fitting a cyl stat is an absolute disgrace they are not exactly expensive or difficult to wire and fit!

So I am not sure how I identify flow and return unless the installer wrote it on the pipes. I will have a look when I can.

the flow will be the first to get hot but at the moment everyone is second guessing we really need to know the exact layout of your system, if you are logged in then click on the images tab under the main heading then you can upload photos stored on your computer,persuming you can take a photo then transfer it to your PC first

Matt

 

[SquiddlyDiddly]

Answering all questions - I hope.

Boiler is a Worcester Greenstar 30 CDI.

I know where the pump is but I didn't know how to tell if it was on the Return or Out side.

From the photographs you may be able to see the vent pipe coming out of the exit central heating pipe from the hot water tank. The feed pipe has the gate valve just below the bottom of the header tank. There is also a cold water tank at the base of the hot water tank in the picture.

 

[45yearsagasman]

SD, Just had a look at your pics and that is a disgraceful installation by a complete bodger who had no clue about system design. All the ptfe tape on the compression joints is a giveaway. I would suggest getting a reputable firm in to start again. There are too many faults there to explain let alone guide you into fixing them.