If there is I understand the problem. What if there isn't?
The threaded fittings on the bottom of the cylinder for the mains coming in and the water going out appear to be identical, and very short. If there is a non return valve it would almost have to be inside the cylinder. Don't know anything about manufacturing processes of steel cylinders or the size of non-return valves, but that seems a bit unlikely. Instructions didn't say anything about fitting a non-return valve on the mains feed, cos if they did we would have done it.
What do you mean by temperature relief? How does this differ from the cut out on the immersion? Also I would have thought that the French ones would have a cut out on the immersion too but I don't know. Why are we assuming that they don't?
Have you ever seen one of these cylinders? The cylinder itself is within a metal casing with the insulation in between the layers. They are too high up for me to see the detail on the top and there does seem to be a removable section on the top of both, but even if one could get at the cylinder inside, how would one fit the pressure relief valves if the fittings were not already on the cylinder?
These cylinders are fitted in almost every home in France. If they were in the habit of exploding and killing people I think we would have heard about it. I suspect there are more safety features built in than we are aware of. I will try to track down the plumber....
The high pressure releif valve is usually at the top. This can usually be removed and a tee inserted and two valves fitted. If you only have one and it failes (seized) then the other kicks in. Each year both must be tested, usually be turning the knob on top.
Blending does not scald. They are to be mandatory in the UK soon.
Starting a new thread in the hope that someone else will answer my initial question...
Also the attributions were a bit mixed up so I will add who said what....
IMM said:
IMM said (missing the point)
I really can't decide if this is a serious answer or if you are trying to wind me up. Just suppose my theory were correct (which I admit is unlikely) I would have thought that fitting one would be the last thing I would want to do!
Another questi> > The threaded fittings on the bottom of the cylinder for the mains
I have since discovered that they do indeed have a cut out in case of high temperature or there being no water in the cylinder.
IMM then suggested:
Holly asked:
I still doubt that..
To which he didn't reply, but never mind, it wasn't a very serious question, was just wondering what he would suggest.
IMM said
Holly said:
IMM said
No, it appears that on these cylinders they are usually at the bottom, as I and others have said.
Fair enough
IMM said:
Neither do mixer taps on the whole.
Are they? I would prefer to be given the choice. Except where there are very young children unsupervised, elderly people etc I think the availability of hot water is useful. Blender valves could and should be fitted where necessary, I don't see why the rest of us can't be trusted with 60degC water.
This is what happens in some other lands. The other alternative is that the pressure/expansion relief valve opens and dumps the increased water volume into the drain.
However, our splendid UK Water Regulations prohibit the waste of water (so we have expansion vessels) and the expansion of water back up the mains, to prevent contamination (so we have check/non-return valves).
An unvented cylinder should be supplied as a unit (assembled) or a package (all safety devices assembled, all the other control components loose for site installation). The controls on the inlet will include a pressure reducing valve, a strainer and a check valve.
French cylinders might not have a check valve, legal UK ones must have.
Ignore him.
Ignore him.
The pressure relief valve is correctly but pedantically called the expansion relief valve. It is often fitted on the cold inlet pipe, after all the IVs. There should also be a combined Temperature and Pressure relief valve (T&PRV). This must be fitted in the top (hottest bit) of the cylinder since it's primary role is to open fast & dump excessively hot water if the temperature controls fail. It also has a useful secondary role as an additional pressure relief valve.
Let's not be daft about this. It's got to have a correctly-sized combined T&P relief valve fitted (i.e., factory fitted) in the cylinder. If it hasn't got one, or got screwed boss for one, it's not suitable. You're not going to try drilling and tapping a pressure vessel, are you?
It is an offence to > > These cylinders are fitted in almost every home in France. If they
There should be 3 safety devices on the LTHW heater and 3 safety devices on the electric immersion heater. You have to seriously abuse them to get all 3 devices to fail, but it does happen, they can burst/explode and they have burst. You may not have heard about it, but it happens.
IMM said
Ignore him.
Are they?
Yes. The thermostatic mixing valve manufacturers' association has a pressure group. Scalding is a hazard.
You can always remove them but then it's down to you.
In short two pressure relief valve, which is what I suggested for the French cylinder.
It is clear you not very experienced, despite attempting to pass yourself of a pro. Your previous terminology of weather compensation clearly indicated that.
Appears so (blending valves) .
..and scald the kids. I know of at least two children that jumped into scalding hot baths and required hopital treatment. The hot was run first to add cold and they just jumped in before they should have.
One pressure relief valve and One temperature & pressure relief valve.
The latter uses a fluid which undergoes a phase change (i.e., solid to liquid, I think, but could be liquid to gas) and so a large volume change at the specified temperature. This causes it to go from closed to fully open in a very short temperature range, i.e., very fast, and discharge the excessively hot water. It is not to be confused with a pressure relief valve. The T&P relief valve does also function as a pressure relief valve (if the expansion/pressure relief valve has already failed), but this is a useful secondary role.
If it hasn't got a T&P relief valve, and there is no suitable French Connection, give up.
Ignoring him is the best policy. I will only bother correcting him if he starts getting dangerous.
That is the UK regs. The idea was to get extra safety on a one pressure relief system.
If I recall correctly, There is only a requirement for one of each, the temp valve and pressure relief valve. The temp just doubles up as one. I don't think every makers uses the double temp/pressure valve.
You haven't corrected anything yet., oh know-it-all.
That sounds about right. still want to know about plastic pipes?
I've just read the original thread & will try to answer some of the original questions.
CORGI registered installers are registered to work on gas. Unvented HWS system installers will have a CITB or IoP issued card (there may be other certifying bodies). CORGI registration is NOT a qualification to install unvented HWS systems.
You are obliged by the Building Regulations to notify the local authority if you install an unvented HWS system >15 litres. You have to inform them of;
1) the make, name, model and type of system.
2) The name of the body (i.e., BBA number) that has certified that the system complies with paragraph G3 of Schedule 1 (Building Regs).
3) The name of the body that issued the registered operative card to the installer.
The drain pipe has to be metal. No plastic pipes are rated to handle water at 100 degC AFAIK. It will melt and tip boiling water on the floor. It has to be piped outside the building to a place where it is safe and visible. If it discharges water, it is alerting you to the fact that there is a fault on the system that needs to be rectified.
No, Qieno Sabe. The size of the pipe is determined by it's length and the number of elbows in it, to ensure it is capable of carrying away all the water discharged from a relief valve. You may be required to install a 54mm metal discharge pipe, or it could be impractical to install the cylinder as proposed.
BS. It is to manually open the valve. You can sometimes use this to replenish an air bubble, but that is not the sole purpose of the lever. The lever types have generally been superseded by relief valves with knobs, which do the same thing.
The tundish/funnel collects the discharges from the two relief valves and funnels them into one metal drain pipe. It allows you to see whether either of the relief valves is discharging or dripping. If the discharge is water at >100degC (yes, that is right, if it's under pressure it can exceed 100 degC) it allows some steam to flash off, so the discharge is at 100degC or less from then on.
The final connection to the immersion heater has to be wired with heat resistant flexible cable, the size depends on the kW rating.
The A-C system imposes a small dc voltage on the steel vessel to inhibit galvanic corrosion. They used to be fitted with a sacrificial anode, which did the same thing. I believe that sacrificial anodes are no longer permitted because they're meant to corrode & drop their corrosion products in the potable water.
caused
Any approved UK unvented system would have a check valve. Many stopcocks have the washer mounted on a loose ?jumper' which acts as a check/non-return valve. You'd have to ensure that there were no check valves, or one-way stopcocks on your mains supply, and that no-one fitted one in the future. Even if you did this, it's quite likely there would be a check valve or one-way stopcock in the water supplier's connection under the pavement.
Right, I'm with you now, thanks for the explanation. See also my reply to your other message.
In any case I only remembered after asked the question that often cold supplies except for kitchen tap come from storage tanks anyway. Had looked at the layout here and forgotten the various previous systems we have had.
I was being daft deliberately, obviously didn't make that clear!
That was the point, I thought IMM might be suggesting exactly that!
There are vented cylinders available here in France, but it would appear that not all of them are vented. So the OP would need to check first. Peter Cherry, if you are still reading, I found some details on the web the other day but don't have them cached, I think they were at
That's what I thought. A local plumber installed the system for the previous owner.
Thanks for that. Given its location here it wouldn't matter too much if it did tip the water on the floor. Which is lucky because the alternative would be to drill yet another hole through a 3ft thick stone wall and having done a couple of those recently I don't think we want to do another one! I guess this is why the plumber didn't do it in the first place. The problem of course is that at the moment it isn't visible so we would not be alerted to a fault. Will have to think about an alternative system. The only thing that springs to mind just now is something like a sink trap which would collect water in the bottom but we will give it some more thought. Or get out the Hilti drill again......
Then the OP would need to ensure that he could get access to the point where the factory fitted cable, which (from the point where it leaves the body of the cylinder at least, it might be different inside the cylinder I suppose) appears to be ordinary three core 2.5mm cable. We have recently had new cabling put in to replace ours (also to even out the load on the three phase system but that's another story!) but it's not connected it up yet - another job for the xmas holidays.
OK, thanks.
OK, our case is very unusual. We don't actually have mains water at all, we have a gravity fed supply from a spring fed well further up the hill. We also don't have a storage tank in the attic, so we have a direct cold water feed. The stopcock on the old house (with HW cylinder with dodgy plastic overflow) is definitely not a one-way one. However, the new stopcock which we fitted recently to the little house next door might be. I will need to check to find out since this one supplies the new cylinder, the one with no visible pressure relief system.
You should have said that in the first place. The check valve may have been deliberately taken off so as to expand up the line to spring. I would certainly fit an anti-vacuum valve on the top of the cylinder. If the cylinder boils the expansion will go backwards and the anti-vacuum valve will open to prevent implosion.
There will be a connection that the existing relief valve is connected to. A brass tee can be installed with brass barrell nipples, etc, on this to add another temp relief valve.
The tundish should be within 500mm of the temperature relief valve. Another function is that it allows the relief valves to discharge if the outlet pipe becomes blocked or restricted (freezing, physical damage, limescale, blockage). This would discharge over the floor, but not as much as the cylinder splitting under pressure. There's quite a lot of other requirements for the discharge pipe alone.
Either the tundish or the external discharge has to be visible; having both visible is ideal.
The factory fitted 3 core probably is heat resistant, there's not much, if any, visible difference.
Sounds interesting, not many spring fed systems in London. Your proposals sound like quite a lot of trouble, compared to just fitting an expansion vessel. I'm not certain the Water Regulations prohibition against wasting water apply to wasting your own spring water, so you could just let the expansion relief valve discharge it. The expansion relief valves are liable to start dripping after discharging, due to bits of limescale getting under the seat & then neeed to be replaced. I'd go for an expansion vessel.
As I have already said, on one of these cylinders, as far as I can see, there isn't!! Nothing, just cold feed coming in as per in the installation diagram which came with it.
OK so a tee could be added just at the point where the cold feed comes in, with the valve as you suggest. This would seem to be a good idea. We have to do some plumbing on that system at some point anyway to add a pump to circulate hot water from the woodburner through the coil, so we might do that at the same time. On the other cylinder there is the PR valve and it is on the bottom, teed off the feed pipe, so yes, I suppose it would be possible to add yet another tee to that.....
When it boils it has to go somewhere, so it goes back up the cold feed. With no water replacing the water moving back up the cold feed the cylinder will implode. The anti-vacuum valve will prevent this.
Not really. My initial question was a general "what is the issue here, why can't it expand back up the feed pipe?" question.
I think with the cylinder in the old house the system was just built that way in the first place, I no idea whether a check valve was removed for that reason, I doubt it. This is the cylinder with the pressure relief valve teed off the cold feed and which drains into the plastic pipe. On the second cylinder, which we fitted, according to the instructions, there is no check valve unless it is in the body of the cylinder, which I doubt.
You are going round in circles here. As I said before, there is nowhere to put the fitting into the top of either of these cylinders. I'm sure you're not really suggesting we should drill and tap in the fittings are you?
expansion go backwards??!! but I know what you are getting at....
so why wouldn't it either not expand further in the first place when it reached that state, or simply suck the air/water/steam back in again??
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