Do I need a new expansion vessel?

[youmother]

Hi,

I have a Heatslave 15/19 oil fired combi boiler.

The boiler is slowly losing pressure...I am not sure where though. The pressure relief pipe that goes outside is dry.

I have pumped air into the expansion vessel and when I do I can hear water bubbling and gurgling in the tank. I unscrewed the flexible pipe that screws onto the vessel and then removed the vessel.

I emptied as much of the water out of it as I could, and the water that was left was black dirty water.

The flexible pipe that screws onto the expansion vessel, where does it come from? There was water coming from the pipe - is it supposed to?

Do I need to replace the expansion vessel or is the problem coming from the pipe that screws into the vessel?

Any advice greatly appreciated. Thanks Matt

 

[Mrmethane]

Hello
I am not familier with your appliance, however expansion vessels are installed to take care of expansion within your heating system has the temperature increases. The flexible pipe most likely connects to the heating system within your appliance and yes water should come out of it draining water from your system.
If you are losing pressure (a drop showing on your pressure gauge) then you have a leak somewhere on your system, this could be anywhere and could be quite small. If you have seen water leaking around the expansion vessel then investigate further to determine that it is leaking and have it repaired.
When you have reinstalled your expansion vessel it has to be pressurised with air in a specific way, and to a specific pressure. This is very important and should only be done by qualified and trained persons used to dealing with expansion vessels on your particular appliance.

 

[youmother]

Thanks for that.

But should water be in the expansion vessel itself? Because if not, the pipe that goes into vessel has the water coming out and surely that goes into the vessel?

In the past water has leaked through the top of the expansion vessel, and it has also come through the valve at the top (where I would pump it up) but since then had seemed to be ok until I recently noticed the drop in pressure.

Do you know how I should re-pressurise the vessel? Do I do it before I reinstall it or do I do I do it when it is out? Because if it is out it won't re-pressurise as the flexible valve isn't screwed on so air will just escape!
Thanks

 

[Axel]

If there is water coming out of the Schroeder valve, then the expansion vessel is £ucked.

 

[holty]

probably just needs recharging with a foot pump. and yes water should be coming out of the flexi. also check the aav on the top of the boiler to the front left near the plate heat ex. usually these let by. more so if you retop the boiler, after its drained down.

 

[Mrmethane]

Hiya

Yes water should be in the expansion vessel, it contains a bladder like the ones in old footballs. This is filled with air and the rest of the expansion vessel is filled with water. Water does not compress but air does, so has your system heats up the water expands and compresses the bladder so expansion vessel. This prevents the water from expanding and bursting through the pipes or heat exchanger etc.
As I said before I don't know what pressure your vessel should be pressurised to, maybe the boiler manufacturer can help with that, but you do have to pressurise it in situ.

 

[youmother]

So is it as simple as putting a new one in? I know there could be 101 things that it could be, but with the expansion vessel knackered, will I need to change anything else or just a straight swap? Obviously if it still loses pressure it will be something else.

I have had a quick look on the net for a vessel, and a like for like replacement (12l rectangular vessel) is near enough £100.

There are other vessels that are the same size in terms of volume and are uch cheaper but they wouldn't fit inside the boiler - I have read that I can fit it externally to the boiler but not sure how I would actually do it? And whether I should or not.

 

[holty]

yep not cheap. 1 bar charge pressure should be ok for your old vessel. you could fit one external, preferably near the return.

 

[youmother]

Thanks for that.

You mention that I need to position it near to the return? What is the return?

Someone mention that I should check the aav...what do I check?

Also on the top of the boiler there is a gold part with a black plastic screw on the top. It has 10 bar written on it. What is this as when I refitted and repressirised the vessel air was coming out of it intermittently. Thanks again.

 

[holty]

Also on the top of the boiler there is a gold part with a black plastic screw on the top. It has 10 bar written on it. What is this as when I refitted and repressirised the vessel air was coming out of it intermittently. Thanks again.

that would be the aav i mentioned. the return is the heating return. most commonly tapped into the bottom of the boiler at the rear. or teed in to the top of the boiler. look on the worcester website they do have the manual for this boiler. it will then give you and idea of installation.

 

[youmother]

Yes I have the manual which I printed off, and trying to use that as a guide but struggle sometimes to work out which parts are which when looking at the boiler and looking at the manual.

I think I now need to make a decision of whether to go for like for like vessel or go for an external one. The amount of space around the boiler might make me have to go for like for like.

Should air have been coming out of the aav intermittently when I had repressurised? Is that what it is meant for?

I have been reading the FAQs on here about repressurising the vessel, it says to use to the drain cock to drain water out of the system rather than the pressure relief valve, but where is the drain cock?

Thanks again.

 

[youmother]

I know where the drain point is - is it the same thing - the only thing is it is in an awkward place (really close to the floor so can't get anything under it to catch the water. I don't have any pipe that will fit to it, any ideas?

 

[Burnerman]

Its much better to replace like for like, if you can - in my opinion. Depressurise the system by opening a radiator bleed valve. as soon as the pressure is zero, no more water will come out and the gauge will read '0'. It may take a wee while.
You can then undo the flexible pipe to the expansion vessel, and unbolt it from your boiler. There will be a slight water spillage.
With the new EV, pressurise it with air, using a car foot pump, to the recommended pressure which will usually be between 10 and 14 psi.
Fix the new EV in place and connect the flexy pipe.
pressurise your system via the filling loop to around 1 bar, or whatever is recommended.
Job done!
John

 

[youmother]

Its much better to replace like for like, if you can - in my opinion. Depressurise the system by opening a radiator bleed valve. as soon as the pressure is zero, no more water will come out and the gauge will read '0'. It may take a wee while.
You can then undo the flexible pipe to the expansion vessel, and unbolt it from your boiler. There will be a slight water spillage.
With the new EV, pressurise it with air, using a car foot pump, to the recommended pressure which will usually be between 10 and 14 psi.
Fix the new EV in place and connect the flexy pipe.
pressurise your system via the filling loop to around 1 bar, or whatever is recommended.
Job done!
John

So drain it via a radiator rather than the drain point. I can see why it might take a while! I will go for a like for like as there is no room for an external one without moving around appliances and units...

I did try and repressurise the ev when I removed it and air was just coming out of the hole where the flexible pipe joins so I guess that it confirms the theory that the diaphram is broken.

Thanks for your help on this everyone.

Now to find the cheapest vessel!

 

[holty]

actually seen worcester clamp the braided hose to change an ev on an old 400 highflow. suppose bit like car brake pipes when doing a change.