Diagnose my Tundish Problem ?

[Spinny]

I am getting occasional water discharge through the tundish on my mains pressure unvented cylinder with gas boiler.

(Not 100 percent certain, but this appears to occur when the hot water is on and has been on for a while.)

The mains pressure is about 3.5bar. There is a Caleffi combination Pressure Reducing Valve fitted and it reduces the pressure to slightly below mains. There is also a temperature/pressure relief valve on the Gledhill cylinder. (See photos). +Both are connected to the same discharge pipe and single shared tundish.

- the water discharge is not hot - I have stuck my finger in it.

- I have temporary outside style hot and cold taps piped from the system just 2-3m away from the system. When the tundish runs, the water pressure at the cold tap is about 3.5bar/50PSI. The water pressure at the hot tap is very high at about 6.2bar/90PSI.

- When I open the hot tap the hot water blasts out and I leave it to run for a few minutes to release this pressure. Reconnecting the pressure guage after doing this shows the pressure at the hot tap has then fallen to about 3.5bar/50PSI and the tundish stops running.

- If I open the cold tap it momentarily blasts out - just for a second or so - then runs normally.

 

In the 2nd Photo the pipe connections are: 

- 22mm pipe into the top is the mains water supply

- 22mm pipe out on the right with right angle bend upwards is I believe the balanced cold water supply

- 22mm pipe out on the right below the balanced cold runs to an expansion tank mounted on the wall (Note green stain on this pipe - joint weep ?)

- 22mm pipe out at the bottom provides the cold water feed to the base of the unvented cylinder

The grey plastic is the mains feed pressure reducing valve.

The red plastic is a 6 bar pressure relief valve outputting to the tundish (So I presume this is what is opening under excess pressure conditions)

 

Presumably the red valve is opening as a result of back pressure from the cylinder ??

 

So what is causing this ? Why is the cylinder pressure rising so high, and does this indicate some problem with the expansion vessel, which is presumably there to provide hot water expansion capacity and avoid over pressure ?

 

PS Having a 6 bar and 60deg C 250L hot water bomb in the house would seem like cause for concern ?

 

Help, explanation, answers, how to get it fixed etc greatly appreciated...

 

(PPS Currently have the Hot Water timer on for 2 hrs in the morning and 2 hrs in the evening - temperature of the hot water from hot tap appears to be 60C as expected. But the over pressure seems like it may perhaps be linked to having the hot water timer on. - though it doesn't occur every time - have only noticed the tundish running maybe once every few weeks.)

 

 

 

Edited Thursday at 20:12 by Spinny

[Nickfromwales]

Expansion vessel having no pre-charge is the usual suspect here.

 

It seems the heating of the cylinder is creating expansion, and there’s nowhere for it to be absorbed.

 

Time to isolate the expansion vessel and check the charge pressure so we can help you through the process of elimination. 
 

Regarding the ‘bomb’ issue, relax.

 

There’s been a failure of some sort, and the safety features have done their job; the red T&PRV had opened to relieve the buildup of pressure in the cylinder, functioning entirely as intended to keep you safe   

[Spinny]

Thanks @Nickfromwales

I attach a couple more pics showing the expansion vessel setup.

There is a 22mm pipe run from the Caleffi combination valve up to the vessel. I don't see an isolation valve on this as such, unless there is a way to isolate it at the combination valve.

The system has been running for 2-2.5 years now, installed by our original builders plumber, who never finished installing the water softener which still sits in our lounge.

I had to point out to this plumber that he had not installed any tundish. His response was to claim that - you will never get any discharges from these valves ! No tundish is of course against regs and manufacturer installation guide so insisted he fitted it.

From the label the expansion vessel states it originally had a 3 bar precharge, and seems to be a 22L nominal capacity - is this sufficient in size ? (I see 4%-9% water expansion mentioned via google and the cylinder is 248L, so seems to be at 9% ish, and not sure whether that capacity is reduced by the air that should be in there)

 

 

 

[Spinny]

Found the install manual for the expansion vessel - attached.

 

According to the drawings at the back of this document, the smaller Zilmet expansion vessels like mine do not appear to have a 1/2inch BSP male connection at the top to enable the actual charge pressure to be measured/adjusted ??

Ultrapro-IOM-V5.pdf

[Marvin]

Hi @Spinny

 

Lots of alternatives here for you to consider...

 

You said a lot when you wrote that the drips in the tundish were cold in my opinion.

 

I would have questioned if the cold water pressure reducing valve (PRV) is working correctly.

 

If you needed a water softener it suggests that the water is hard and this can cause limescale buildup. 

 

If the hot water is under a lot of pressure when first turned on but when left to run reduces in pressure and slowly increases when shut off again it suggests the PRV is letting a small amount of water pass through all the time.

 

Sometimes water pressure can run out of the cold and into the hot when a tap is turned on so I think both having high pressure should be ignored at this point.

 

What you need to do is have the softener installed for sure. It must have been planned for a reason...

 

As for the expansion tank. If it is set at 3 bar, then anything below will not fill the expansion tank, anything above will start to fill the expansion tank.

 

I hope this helps

 

Good luck 

 

M

 

 

[Marvin]

Hi @Spinny

 

Simple tests you can carry out:

 

If the expansion tank is connected uninhibited to the hot water pipe I would turn the cold water supply to the tank off run a tap until there is no pressure in the hot. make sure no one uses the hot water for say an hour. then turn hot tap on. What is the result?

 

If there is no pressure then the problem is related to the cold water.

 

However if there is pressure it could mean there is a problem with the hot water OR the cold water.(some taps will allow water to pass from one to the other supply when pressures are greatly different even when off - perhaps I use too cheaper taps 😂)

 

Turn the cold water supply to the house off this time. do the same to the cold water.

 

If there is no pressure then the problem is related to the hot water.

 

However if there is pressure it could mean there is a problem with the hot water OR the cold water.

 

Good luck

[SimonD]

1 hour ago, Spinny said:

Found the install manual for the expansion vessel - attached.

 

According to the drawings at the back of this document, the smaller Zilmet expansion vessels like mine do not appear to have a 1/2inch BSP male connection at the top to enable the actual charge pressure to be measured/adjusted ??

Ultrapro-IOM-V5.pdf 2.94 MB · 0 downloads

 

At the top of the expansion vessel will be a car tyre type valve which is used to adjust pressure in the vessel.

[Nickfromwales]

Good point by @Marvin about the softener defo needing putting in to prevent limescale. Is this notable on any of the shower heads or taps atm?

 

Can't rule out the possibility that this is causing a failure of the pressure reducing valve (cylinder control group that the expansion vessel is plumbed Into) by crud building up on the valve seating. May be best to strip this down and descale it with something suitable so it can be eliminated from your enquiries.

 

As said, the test valve is right at the top of the expansion vessel. It is sometimes hidden under a black plastic dome cap which screws off to reveal the valve; a Shraeder valve like a car tire.

 

There is no isolation valve for the expansion vessel as your generic G3 installer will have known thats not allowed (by him simply following the installation guide that came with it). You cannot have a means of inadvertently isolating the expansion as its then dangerous to operate it without such protection. 
 

You can buy a cheap pressure tester off Amazon and test the precharge pressure, and to do this you just turn off the cold mains and open a hot tap (making sure the boiler and immersion are both switched off purposefully). Leave the hot tap open whilst you do the test and note your findings. 
 

Test it before, during, and after. Make notes for discussion here. 
 

Close the hot taps, switch the water back on, and then go and run the hot taps briefly to get the spluts of air / water out, to recommission.  

[Spinny]

3 hours ago, SimonD said:

At the top of the expansion vessel will be a car tyre type valve which is used to adjust pressure in the vessel.

Thanks Simon, yes I see now the top cap unscrews to reveal the valve.

What is the best guage to use/buy to take the pressure ? (My current guage only has a tap type screw fitting) Perhaps better to buy one with a pump as well ?

 

So for the 6bar pressure relief valve to open the pressure in the cylinder and in the expansion vessel is likely reaching 6 bar. The expansion vessel should be absorbing the expansion and limiting the cylinder pressure to 3bar or so. Would seem to imply either:

(a) The expansion vessel diaphragm has failed and so the vessel has filled with water

(b) The air pressure outside the diaphragm is too low, perhaps from a leaking valve or vessel

The vessel has a 5 year guarantee, so would seem odd for it to fail in either of these ways in just 2/3 years ?

 

From the manual...

''Some pressure loss is to be expected and should be rectified to within a reasonable accuracy but a significant drop in air pressure may signify that the vessel membrane is nearing the end of it’s life span and may require replacement.''

The manual also states the max operating temperature for the butyl membrane is 70C, so presumably if it has become over heated at some point this may have caused early failure. (Doesn't seem much margin for error when the cylinder is set at 60C).

 

Not sure what the impact of no water softener may be over 2 years.

[Spinny]

18 minutes ago, Nickfromwales said:

Can't rule out the possibility that this is causing a failure of the pressure reducing valve (cylinder control group that the expansion vessel is plumbed Into) by crud building up on the valve seating. May be best to strip this down and descale it with something suitable so it can be eliminated from your enquiries.

The pressure reducing valve was stripped down only about 4 months ago because of concern about whether it was restricting water flow. There was nothing significant found on the strainer and the little that was there washed off before replaceing it. I did notice that after the plumber that did this had finished, the static water pressure at the tap and our shower flow problem were improved. I took this to mean he had tightened/set it less than before so it was acting as more of a 3.2bar PRV than the 2.8bar we seemed to be getting before. As this was giving us noticeably better flow and didn't seem too far from 3bar I have left it alone since then (rightly or wrongly).

[Nickfromwales]

10 minutes ago, Spinny said:

I did notice that after the plumber that did this had finished, the static water pressure at the tap and our shower flow problem were improved. I took this to mean he had tightened/set it less than before so it was acting as more of a 3.2bar PRV than the 2.8bar we seemed to be getting before. As this was giving us noticeably better flow and didn't seem too far from 3bar I have left it alone since then (rightly or wrongly).

This is a major worry! 
 

You need to know exactly what the pressure leaving the PRedV is. Sometimes you can buy a 1/4” gauge and fit it into the blanked off port on the control group, but yours doesn’t appear to have a plastic blanking plug to use to fit this? Can’t see both sides of the valve. 

[Spinny]

So the hot water timer was set to come on for an hour at 4pm today. At around 4:40pm I noticed the tundish going again - so same problem. Static pressure before opening at the hot tap was 90 PSI again etc. Same short burst of water from the cold tap before it goes to normal flow rate. (I should say these are outside taps fitted internally as a temporary job so there is no mixer block or flow restrictors on them).

 

The static water pressure at the outside tap (fed directly from incoming mains) is 50PSI or about 3.5bar.

The static water pressure at the internal cold tap is about the same, but it may be picking up a bit of extra pressure from the over pressure hot side ?

(Water pressure at the internal cold tap drops to about 37 PSI when the hot tap is running - to be expected)

 

I guess even if the mains pressure reducing valve had failed the incoming pressure to the system would only be 3.5 bar, yet clearly the cylinder pressure is getting up to 6 bar when the water is heated. So it must all come back to a failure at the expansion tank.

 

Used a thermometer to take the hot water temperature which was under 60C, so can't be a water overtemp thing or failed thermostat.

Edited 15 hours ago by Spinny

[Spinny]

4 minutes ago, Nickfromwales said:

You need to know exactly what the pressure leaving the PRedV is. Sometimes you can buy a 1/4” gauge and fit it into the blanked off port on the control group, but yours doesn’t appear to have a plastic blanking plug to use to fit this? Can’t see both sides of the valve. 

I can see both sides of the valve because the outside outside tap is connected directly to the incoming mains - I have taken the pressure there a lot of times and it is 3.5bar or 50PSI with very little variation (I have a new 32mm mains pipe connection installed earlier this year to replace the old lead pipe).

 

The inside taps in the utility room only have about 3m of pipe running from the cylinder location. The cold tap is on the balanced cold and the hot tap is from the hot pipe/cylinder.

So pressure readings taken from these inside outside taps are essentially the same as the pressures downstream of the pressure reducing valve. (negligible height difference).

[Spinny]

So I guess you are saying, if the cylinder is running at 3.5 bar rather than 3bar, then this is going to compress the expansion diaphragm even at cold water temperatures (if the vessel diaphragm is only air pressurised to 3 bar) and therefore some of the expansion capacity will be lost.

 

Therefore the expansion vessel pressurisation should be matched to the P reducing V output pressure with a small adjustment for height difference between the valve and the vessel (about 1m or 0.1bar).

[Spinny]

However I have had occasional tundish discharge before the plumber ever came to clean the caleffi PRV. 

So potentially him leaving the PRV set to a higher pressure has simply made the problem worse and more noticeable.

 

 

[Spinny]

2 hours ago, Nickfromwales said:

Good point by @Marvin about the softener defo needing putting in to prevent limescale. Is this notable on any of the shower heads or taps atm?

Only the shower head and one set of basin taps post date the new system - there is a little on the shower head but nothing that impacts flow at shower head or basin tap.

 

The water softener is a PITA because (as you can see) I defo need a proper fully competent, experienced, and conscientiuous plumber.

 

The Water softener is to go in the understairs cupboard but needs to go tight back against the outside wall and tight on one side to a stud wall with the understair loo behind it - otherwise it prevents any meaningful access and use of the rest of the cupboard by blocking the cupboard doorway.

The original builders plumber installed the valve/bypass valve too far over, and also decided to put a standpipe positioned right behind the water softener position and bossed into the u/stairs toilet soil pipe, also necessitating a waterless trap. This arrangement is crap and doesn't achieve what we need/asked for. The water softener itself was never actually plumbed in to bring it into use and the builder and his plumber long ago terminated. Ring another Plumber - Send details/arrange visit - quote promised - quote chased - no quote and availability ever obtainable - ring another plumber: repeat on an infinite basis for 2 years, dry wife's crying eyes, and say don't take the anti-depressants.

A better idea would seem to be to drill straight out through the outside wall with holes for the drain pipe and the overflow pipe. There is no outside surface drain in that position at the moment but it is close to a drain chamber, and it has been suggested to me that a (good) drainage plumber could dig out the hardcore and put one in.

 

Edited 14 hours ago by Spinny

[Spinny]

Just took some water pressures again.

The mains supply is at 50 Psi, and downstream of the caleffi pressure reducing valve is at 50 Psi.

Is it possible that if the plumber that cleaned it didn't reset the screw pressure adjustment properly, and the downstream side has been subject to some 6 bar back pressure, that the screw may have worked out more over time??

because immediately after that plumber had been 4 months ago my memory is that the PRV output pressure was more like 3.1/3.2bar rather than 3.5/50psi, having been about 2.8bar before he started.

 

And in principle is there any reason the system can't be run at say 3.1bar, rather than the 2.8bar it was at before, because even this small change has a very noticeable effect on our shower flow.