Unvented cylinder install - safety concerns. Appreciate advise.

[Quinla01]

Evening all,

At risk of blabbing on i'll try keep this short. I recently replaced an old vented hot water system with a unvented system We went for the Telford Tempest 300L installed by G3 qualified person. Functionally it works well. Pressure is great, heats well, no leaks.

There's still some work remaining to complete the wiring. The guys due in next week. Currently, to turn it on I press a button, completely independent of the cylinder to manually fire on the boiler and heat the tank (in case there's any confusion it's not the immersion) . The thermostat in the cylinder isn't wired to anything yet. It's just a probe sitting in a pocket not connected to anything.

I was told by the installer it's safe to run in this manner until he comes back to complete wiring. Two kids sleep next door to this thing so I double / triple checked with him that's the case and was assured it is. I wasn't entirely comfortable so started doing some homework , I just can't get my head around what is stopping my cylinder from overheating and triggering one of the safety pressure release mechanisms (more on that later). The boiler will remain on until i manually press the button again to turn it off so in my mind, if i were to go to bed and forget to turn it off the water will keep heating until boiling point. I questioned the installer again and was told the boiler (not cylinder) has it's own thermostat that will cut out if it reaches a set temperature. I get that in principle but not sure how its directly related to the temperature and pressure of the cylinder and nowhere I looked suggests this as safety component in an unvented system.

I'm still not convinced so have turned the whole thing off. As a result of doing some homework I picked up on a few other things that I'm curious as to whether are just "best practice" or "absolute must to avoid life chaining injury"

Firstly, the Telford installation manual, a few other threads and potentially building regs seem to stipulate the the minimum straight drop below the tundish should be 300 mm minimum. This means that the pipe that exits the tundish should remain straight for at least 300 mm before bending or turning in a different direction. I guess the reason for the 300mm drop is to prevent boiling hot water / steam under high pressure for coming back up the pipe if it hits resistance. Is that right? Anyway, my turndish is connected directly to a 90 degree elbow (see photo).

Finally, I've read that there shouldn't be any valves, especially shutoff valves between the cylinder and the expansion vessel to prevent someone from accidentally isolating it which i guess is the cardinal sin when it comes to unvented systems. Is that right? Again, my vessel is surrounded by them (see Photo).

I'm hoping you all tell me to chill out, grab a beer and enjoy the rest of my evening as it's all perfectly fine but am worried that's not the case. First and foremost is the safety of my family, but i also assume when come it's first annual inspection it will fail.

Would really appreciate your guys thoughts.

Thanks.

 

[Scott_D]

The discharge after the tun dish is wrong. Water will pour out if either valve releases

 

[steadyon]

1. These cylinders have three levels of safety device:
1a. A motorised valve to turn off the supply of primary hot water, activated by the cylinder thermostat. Not operational on yours.
1b. A pressure relief valve (part of the combination valve) to relieve pressure if it get too high. Operational on yours, but likely to cause a flood because of the incorrect length of D2 pipe before first bend.
1c. A temperature and pressure relief valve. Again, operational on yours but the same problem with D2 length before first bend, but made worse by water being scalding hot.
2. In my view there is an increased risk. While your installer is correct in saying the boiler has its own hot water thermostat, should this fail, then the water in the cylinder could be constantly heated to a high temperature.
3. I would say the risk is in the low probability, high cost of failure range.
4. If it were mine I might be tempted to use it on a temporary basis, but set a timer to remind me to switch it off, and to inspect at regular intervals.
5. However, my children have left home (at last!) and the by the book rule would be to stop using it.
6. That D2 pipe needs to be sorted out, it can't be left like that.
7. I can't see clearly what each valve is doing, but I suspect its OK, since so far as I can see none of them isolates the pressure vessel from the cylinder.

 

[SJB060685]

As above the D2 pipe on outlet side of tundish is wrong, should be a minimum of 300mm straight down before any fittings/bends. Left like that water will splash out over sides of the tundish, it also creates a path of resistance when the idea is to safely and quickly dump any water.
Where as your installer is correct about the boiler having its own thermostat and high limit stat I would not have left it like that. Thermodynamic law states that the temperature of water in the cylinder will only reach equilibrium with that supplied by the boiler, so providing the boiler stats are functioning OK then technically/hopefully everything should be OK, however if the stats failed then temperature can obviously rise.
From what i can see there is still lots to be done, including some safety features and I would not have left the customer in this situation.

 

[Quinla01]

If you had to guess, would you say the installer likely doesn't know the 300mm rule or just doesn't care? Not sure which is worse. If he doesn't know, I could give him a shot at fixing it but then what else has he installed incorrectly that I haven't identified? Knowing and not caring, well that's the kind of thing that makes me super angry. I'd never want to see his face again. Not sure what to do now. These things are so dangerous if not properly. What would you guys do?

 

[SJB060685]

If you had to guess, would you say the installer likely doesn't know the 300mm rule or just doesn't care? Not sure which is worse. If he doesn't know, I could give him a shot at fixing it but then what else has he installed incorrectly that I haven't identified? Knowing and not caring, well that's the kind of thing that makes me super angry. I'd never want to see his face again. Not sure what to do now. These things are so dangerous if not properly. What would you guys do?

If i was to guess then I would say he doesnt know, at least that was the rule when I did my G3.
I'm not an installer these days, however if I was then I would not have left the system like that. What was his reason for not completing on the day?
With regards to having him back, I'm not sure what to advise, maybe someone else has an idea?
He may make right everything, alternatively he may prove completely incompetent and as you are clearly aware an unvented cylinder is not something to mess about with.
Did he even do some basic tests on incoming pressure and flow rates, or did he just say yeah I'll install one for you?

 

[Quinla01]

There was a problem with wiring so he left for the day and had a sparky attend later that day to get the power back on. Next availability for him to come back is next week. As annoying as is not having heating and hot water. I'd have rather he told me not to use it until then then tell me it's completely safe which I don't think it is.

I'd done some homework on supply and flow. We have 6 bar coming into the house so supply wasn't an issue, flow rates with a 4.5 bar pump on the old system was really good so wasn't concerned about that either. That said, no he didn't do any tests himself, but to be honest, nor did any of the other 5 plumbers who gave me a quote and were ready to start work next day.

Another question - when installing these things, is it a case of having done them a 100 times you don't both reading the manufactures installation guide and realistically they're tossed to one side or is it irresponsible to ignore it? Reason I ask is that it does clearly state a min of 300mm in the installation guide. See attached.

 

[SJB060685]

The 300mm minimum is one of many and basic criteria covered when completing the G3 course. It is common knowledge and for reasons stated above should not be ignored.
With regards to ready manuals, any decent installer/engineer will always be reading manuals to stay upto date and further more see if the manufacturer of the appliance being installed, be it a cylinder or boiler etc requires additional compliances. The 300mm minimum is a core basic and to be honest I'm surprised that someone advertising as an installer isn't familiar with it, I'm also equally surprised that no measurements were taken on your incoming supply. Most homeowners hear mains pressure HW cylinder and instantly assume great but if your incoming pressure is poor, or your pipework is not sized for reliable flow rates then the desired outcome is compromised, you then need to start looking at other methods to compensate.

 

[IND_Nick]

As most of the above have covered, the D2 pipe will not work if a safety valve opens fully it will spray/leak everywhere. So that needs sorting.
The thermostat also includes an overheat stat and should be wired accordingly to control the 2 port valve and boiler.
Also the valve on the cold feed under the expansion vessel should not be there as you have noted. There should be nothing to isolate between the cylinder and expansion vessel, it is also not necessary as appears to have isolation before the combination valve.
If I found that in a customers house I would advise it was not used until rectified. A lot of very basic faults, although most easily rectified.
If you do keep using i would agree with above and just run for an hour to heat cylinder and make sure you turn off.

 

[SJB060685]

I missed the isolating valve after PRV. That should be removed and leave the one before combination valve in place. As is will block off one of the safety devices if becomes blocked or closed.
As IND-Nick says all thats wrong is easily put right, although its alarming its like that in the first place

 

[Scott_D]

Where does the pipe go after the tundish?
Outside?

 

[Quinla01]

I'm very grateful for all the comments. It's shocking that something that has the potential to be so dangerous can be installed without being anything other than 100% compliant. We've been doing a bit of building work recently and on at least 3 occasions someone from the local council has come and inspected the work to make sure it's safe. I know people hate regulation as a lot of it is OTT and completely unnecessary but it seems bonkers that something like installing a unvented cylinder doesn't require some sort of independent body to verify it's been installed correctly.

To wrap things up, worst case scenario - it's conceivable that I manually fire up the boiler and forget to turn it off (because i'm knackered looking after a 3 year old and 6 month old all day). The boiler fails to shut off when it reaches a certain temp because it hasn't been tested since being installed 18 months back , the cylinder overheats, the pressure release valve goes (hopefully) and starts flooding, someone goes into the airing cupboard to see what the noise is and why its leaking and are hit in the face with boiling hot water? Wowzers.

 

[Gasmk1]

you boiler should have an o/heat trip

 

[Quinla01]

Where does the pipe go after the tundish?
Outside?

It does yes . That part i knew about beforehand and asked the builders to work with him to punch through the wall.
[automerge]1591549491[/automerge]

you boiler should have an o/heat trip

I think it's reasonable that i should assume this is what he was coming back to install... but who knows to be honest. My argument is that it's irresponsible to allow, let alone suggest that I operate it before the trip is present.

 

[SJB060685]

What he's coming back to install should be the cylinder thermostat and overheat limit stat. This is a combined unit that mounts to the cylinder and is in one of your pictures above. He should also be installing the two port motorised valve.
As it stands the only temperature control you have over your HW is the boiler thermostat, the boiler will also have a high limit stat should the boiler stat fail.

 

[Quinla01]

Thanks again. I think I've come to a decision on where to go from here.

 

[king of pipes]

The guys have covered alot above, in my opinion the installer has become complacent and is not working safely I would not have left it like this all the safety devices should be connected and tested before the cylinder is commissioned and put into use , we all over commit on jobs but that's no excuse for leaving a potentially unsafe installation you are well within your right to report the install to Gas safe who will inspect the install and force the installer to make the alterations needed to comply with the manufacturers installation instructions and the building regulations at his own cost, it maybe worth you sending a email to your installer expressing your concerns and give him the opportunity to meet his contractual obligations to install your system correctly and 100% safely but it's really your decision we are living through challenging times at present so tread carefully but don't be fobbed off you seem a sensible chap, heavy handedness is best avoided but sometimes its necessary especially to protect your family and your property . Regards kop