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

 

[Guardian Angel]

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.

Dear ahoythere,

As one of the other posters commented, the expansion vessel has nothing to do with increasing pressure to your shower. In an unvented system, the power to your shower is provided by mains pressure. The purpose of your white expansion vessel is to allow water in your hot water tank to expand safely.

There's a good article here which explains thermal expansion and how an expansion vessel works.
Thermal Expansion - Learn About - Watts

I recently watched a plumber service my own expansion vessel which had filled up with water and am happy to pass on my notes on the understanding that I am not a professional and if you attempt the job yourself, you do so at your own risk.

To recharge the vessel with air, you will need to disconnect it. First you need to shut off the water supply. Cranking the hot and cold water shut off valves in your pic should do the trick. Then open the taps at the lowest point of your house to release any water in the pipes.

Remove the expansion vessel from the bracket. Turn vessel upside down (to stop water pouring out) with the braided hose pointing upwards and the valve pointing downwards and undo the nut which attaches hose to vessel.

The vessel will probably contain water, so go to a sink or take the vessel outside and invert it and allow all the water to drain out.

Now you can recharge the vessel using a foot pump or bike pump and a pressure gauge. 3 bar (44 psi) should do. If any air is escaping, your vessel is faulty and will need replacing.

Re-attach the braided hose to the expansion vessel. Re-mount the vessel in the bracket. Turn off the taps you opened earlier. Open the shut-off valves you closed earlier. Good luck, take care and if in doubt, contact a professional.

 

[Best]

Good discription of vessel & its use. That's not totally correct way to recharge the vessel, & sounds like guy didn't know. I would be careful to work at unvented units, as the other safety features must be checked. Also, what if it is installed incorectly? Not rocket science, but not a DIY job either. Don't penny pinch, it needs done safely & legally, for a few quid.

 

[Guardian Angel]

That's not totally correct way to recharge the vessel, & sounds like guy didn't know.

Is it any wonder that members of the public come to theses forums wanting to tackle jobs themselves? I paid 'a few quid' and yet you say that the plumber may not have done the job correctly. What am I to think?

The problem with the plumbing profession - like so many of the trades - is one of trust. This forum encourages people - like ahoythere - to engage a professional. From our perspective, employing a professional often feels like a lottery! And reading some of the previous comments posted on here (which appear to have been removed), I can understand why people despair of hiring anybody! We hand over our money and have no idea whether the job is being done properly.

Best - in the spirit of Christmas, why not explain to the readers of this post what you would have done differently, thereby helping to raise the level of confidence in your profession?

 

[billybob150811]

i agree with beat why remove the vessel from its bracket adding air is possable in situ the actual pressure should relate to the pressure in the house not to makers norm

 

[ahoythere]

Thank you Guardian Angel. Very helpful.

I note billybob150811's comment about the actual pressure inside the vessel being less than the amount mentioned in Guardian Angel's post and am interested to understand why it would be less than the manufacturer's 'pre-charge' level. The sticker on my VAREM/Extravarem expansion vessel says 'Precharge 3 bar' and 'Max working pressure 8 bar. There obviously needs to be some air in the vessel to prevent it from totally filling up with water as the water in the hot water tank expands. I can sort of see that even very low pressure (room pressure even) would be enough to inflate the diaphram and provide resistance to incoming water, but my knowledge of Boyle's Law and thermodynamics ends there.