How to top up (recharge) a hot water expansion vessel?

[ahoythere]

Firstly, may I say this: there is quite a bit of info available on the web - including a YouTube video - about how to top up the pressure in a heating expansion vessel (and I know how to do this), but nowhere can I find any information about how to top up the pressure in an expansion vessel which regulates hot water pressure (to showers, taps etc). I am hoping that this forum will shed light on the subject and that the world will thank me...and you! 🙂

To my problem...

I'd like to increase the pressure to my shower. My house is fitted with an unvented heating system. There is a white 'Varem' (Extravarem 12 litre) expansion vessel located just above my hot water cylinder (picture attached). [To avoid confusion, there is also a red expansion vessel fitted near the hot water cylinder which is not the subject of this post].

On the top of the white expansion vessel is a Schrader valve. When I depress the valve, no air comes out which suggests that the cylinder needs recharging. The reason there is no pressure is that I think I let the air escape (doh!) with some cack-handed attempts at trying to top up the vessel. The sticker on the vessel says that the cylinder should be precharged to 3 bar and the max working pressure is 8 bar. I am reasonably confident that there is nothing at fault with the expansion vessel or the Schrader valve.

Please could someone explain how I go about recharging the expansion vessel and how much pressure to put in it. When I tried to do this earlier, I closed off the two red handles marked 'Hot Water Stop Valve' and 'Incoming Water Main Stopcock' (see picture attached), opened all the hot taps in the house, but still found it impossibly difficult to pump air into the vessel. I'm obviously doing something wrong!

I have taken a couple of photos showing the expansion vessel and the hot and cold cut-off valves and would be very grateful for expert advice.View attachment 4485View attachment 4486View attachment 4485View attachment 4486

 

[dontknowitall]

Firstly, welcome to the forums!!

In my opinion, I'm afraid it's too dangerous to give you the instructions and know how to fix this. Unvented cylinders must, by law, be maintained and installed only by those who have an unvented "ticket". This is a similar sort of scheme to electricity, gas and some parts of oil installations. Unvented cylinders are dangerous if not working properly and the expansion vessel is part of the safety mechanism.

If you say where you live there might be someone here who can see you and sort it out or you could try some local plumbers - ask if they are qualified to work on unvented cylinders as not all plumbers are.

The good news is that is should be a quick fix. The plumber will probably want to check other parts of it are safe but this doesn't take long.

Most jobs we can help you with on the forum without having to visit or suggest calling a plumber so if you have other problems in the future you'll find we are much more helpful than in this case!!

Hopefully it will be sorted out quite quickly for you.

 

[ahoythere]

Hi dontknowitall,

Firstly, thanks for the swift response. I respect your opinion that this is a job best left to a professional, but I thought the purpose of these forums is to share knowledge so that people have an alternative to hiring a professional, or can at least assess for themselves the level of risk/difficulty that a job involves and whether to tackle it themselves or get a professional involved.

I would be pleased to hear from any other forum contributors who are willing to shed light on this topic.

 

[PlumbBobBob]

you are quite right this forum is for sharing knowledge except where it relates to safety critical components, when we tend to clam up really. sorry but for safeties sake you really need to get someone in to do this for you

 

[Best]

Afraid I agree with above comments. It is not too difficult to pressurise the expansion vessel, but has to be correct pressure, & the entire unit & valves need checked also. Shouldn't cost much to have it serviced, which has to be done yearly for safety, correct operation & warranty - usually 25yrs. They are a bomb, if worst ever could happen, ( see videos on utube about them! ).

 

[Hardy1]

not being rude in anyway(before sum one says anything) but for sumone that is uncompetent in unvented hot water systems-how can you assess the level of risk if you do not know what to assess, just like above these things are time ticking bombs in the wrong hands-but in the correct hands- they can give you a very good amount of pressure and flow rates on baths and showers chuchking a good bit of water at you- (with peace of mind knowing that nothing wrong can happen. we can only advise you-get a registered person in with a unvented ticket- they will sort it.

 

[dontknowitall]

Ahoythere

I acknowledge your frustration, which is why I took time to write a more lengthy reply rather than just post "Get a plumber in". If you want to do this yourself you can attend an unvented course and obtain your ticket and there's nothing to stop you doing this!! This is what plumbers do as part of the process to obtaining their ticket.

When it comes to other things on this forum like taps or wondering if the pump isn't working we do try and help and the first response is NOT "Get a plumber in".

As a side note, if I told you what to do, you did it, then left the house for the afternoon, how would I feel if it later transpired that another member of your family was alone in the house and died from an explosion? Not caused by curing the immediate symptom but by me not knowing that an unrelated valve was faulty and not telling you what to look for, how to test it, etc, etc. And how would I feel if I knew someone had died from me posting a comment to help someone but choosing to ignore the risks involved? Unvented cylinders set up incorrectly are potential bombs and that is no exaggeration.

Life is too important to risk by posting a few comments on the internet to try and help someone, short cutting the proper way of doing things.

It is frustrating, but the more responsible plumbers on this forum are not going to post irresponsibly.

And, as I said in my first post, I hope you get it sorted easily and quickly. If the problem is what I think it is, it's an evening job for a plumber on the way home from his (or her!) day's work.

 

[ahoythere]

Life is too important to risk by posting a few comments on the internet to try and help someone, short cutting the proper way of doing things.

Dontknowitall - you could make the same argument for any and every post in this forum. Someone who is incompetent could act upon the information you give and end up causing injury to themselves and others. Such is the nature of DIY.

I understand that you want to draw the line somewhere but from where I sit, it's difficult not to form the impression that the primary purpose of this forum is not to pass on knowledge, but to further the interests of the plumbing profession. The whole idea of a forum is that people pass on their knowledge FREELY - not tell people to go and find a plumber.

As for Hardy1's comment - how can I assess the level of risk without knowing what to assess etc, it's all about knowing your limitations, isn't it? Someone may be unqualified, but that doesn't mean that they are not up to the job. I found out how to recharge the heating expansion vessel on my unvented central heating system by looking up the information on the internet. It's a job I have done many times and I'm still here to tell the tale!

I find it difficult to believe that recharging the hot water expansion vessel on my unvented heating system is beyond the wit of a competent DIY-er. I guess that's where we must leave it although I would of course be grateful to hear from anyone who is willing to pass on their knowledge and will not have a sleepless night about having done so.

 

[dontknowitall]

Last time I checked, there was a difference between injury and death.

 

[dancinplumba]

Ahoythere

I acknowledge your frustration, which is why I took time to write a more lengthy reply rather than just post "Get a plumber in". If you want to do this yourself you can attend an unvented course and obtain your ticket and there's nothing to stop you doing this!! This is what plumbers do as part of the process to obtaining their ticket.

When it comes to other things on this forum like taps or wondering if the pump isn't working we do try and help and the first response is NOT "Get a plumber in".

As a side note, if I told you what to do, you did it, then left the house for the afternoon, how would I feel if it later transpired that another member of your family was alone in the house and died from an explosion? Not caused by curing the immediate symptom but by me not knowing that an unrelated valve was faulty and not telling you what to look for, how to test it, etc, etc. And how would I feel if I knew someone had died from me posting a comment to help someone but choosing to ignore the risks involved? Unvented cylinders set up incorrectly are potential bombs and that is no exaggeration.

Life is too important to risk by posting a few comments on the internet to try and help someone, short cutting the proper way of doing things.

It is frustrating, but the more responsible plumbers on this forum are not going to post irresponsibly.

And, as I said in my first post, I hope you get it sorted easily and quickly. If the problem is what I think it is, it's an evening job for a plumber on the way home from his (or her!) day's work.

well said,
steve

 

[Hardy1]

if you know "how to recharge your hot water exapnsion vessel"-what other knowledge would you like us to tell you freely ?

 

[Simon F]

you stated in your post that you wanted to increase pressure to the shower. the expansion vessel does not change the pressure to your shower, by definition it takes up the expansion in the hot water, preventing the tank bursting. the fact that you are asking the wrong question shows that you should not be attempting the job. as the expansion vessel is uncharged, you should turn off any forms of heating to the tank until it has been properly serviced by someone legally qualified to do so

 

[markfxy]

get a plumber in

 

[dancinplumba]

make sure he has his g3 tho lol 🙂

 

[Hybrid]

-

I understand that you want to draw the line somewhere but from where I sit, it's difficult not to form the impression that the primary purpose of this forum is not to pass on knowledge, but to further the interests of the plumbing profession. The whole idea of a forum is that people pass on their knowledge FREELY - not tell people to go and find a plumber.

A forum is somewhere where people can discuss things of mutual interest. This is a plumber's forum where plumber's discuss aspects of their trade.
It's also, by the good graces of it's membership, a place where the public can often benefit from the knowledge and experience of professionals. Knowledge which would at any other time come at a price.

We can help you with many other plumbing questions but not this one.
You cannot legally work on a safety feature of an unvented system without an unvented ticket. You need to get a suitably qualified plumber in.

 

[ahoythere]

Hybrid - your comment says it all. A plumber's forum. Maybe it should be renamed: theanwerscallaplumbernowwhatsthequestion.com?

Simon F - thank you for your constructive advice which I found really helpful. Funny how no-one else pointed this out. I did wonder about whether the expansion vessel has anything to do with the pressure of the hot water flow. If there is no air in the expansion vessel, what can happen exactly?

 

[Hybrid]

If there is no air in the expansion vessel, what can happen exactly?

The hot water will have nowhere to expand so the pressure builds. With a buildup of pressure the boiling point of water increases.
As the pressure increases the cylinder could rupture causing your water above 100 degrees to flash to steam and expand by 1600 times. Your house will look like somethng from the blitz.
Get a plumber in.

 

[Best]

Think the problem we plumbers have with you asking advice, is that we have to be trained & registered & obey rules which are there to help remove any danger from unvented units, & therefore it would be reckless to tell someone to DIY it. It is also law.Most of us have seen the results of lack of knowledge on plumbing. I recently saw a sealed heating system that exploded when all the safety features were neglected. An unvented unit is more dangerous, as it is one unit.

 

[billybob150811]

i dont think the intention is to be rude as such but a little knowoledge can be a dangerous thing the pre charge is usually 3 bar but you shouldnt read anything into that its just what makers do from memory water boils at 160 degrees at 3 bar and expand 8000% at atmospheric pressure so remote as the chances of hurting yourself are they could be serious and you cant blame people for not wanting you to hurt yourself a service might reveal debris in the strainer or prv set low so it may pay to get an expert in to view the system as a whole

 

[REDSAW]

just an example.

Mythbusters - Water Boiler Explosion in House - YouTube