Heatrae sadia megaflow problems

[musgrove]

I am site manager of a block of flats in sunny glos. We have 35 off heatrae megaflow d 145 immersion heater tanks, half of which have leaking overflows which are damaging the fabric of a grade 2* listed building, formerly the largest woollen mill in the county. I have regenerated air pockets in line with instructions from HS tech dept, fitted non return valves in the hot water outlet pipes to prevent cold water back feed from shower mixer valves, changed thermal/pressure relief valves, all to no avail. I monitor the water pressure on site, which has a PRV limiting the pressure to 3 bar. The water temp is set to 60 - 70C.I am in danger of losing my sanity trying to stop these overflows from leaking. I have exhausted my patience with Heatrae Sadias tech dept, and i now know more about these systems than the 3 different plumbers who have tried to find a solution. Can anyone out there help, please?

 

[tamz]

You could fit an external expansion vessel (white ones for hot water).

 

[justlead1]

Hi. Sorry to here of your problems. What form does this statement take?( which are damaging the fabric of a grade 2* listed building,)

 

[tamz]

Probably staining the walls.

 

[gaspastemania]

Overflow????
dont you mean the blow offs are passing water on the megaflow as its unvented!!

 

[Dannypipe]

PRV's are definetly doing their job? Have you actually checked the pressure after the valve?

As said, additional expansion vessels could probably solve the issue. You only have to try repairing the one unit, and you'll have the problem pegged for the whole lot.

Do they lose water at the tundish when the cylinder is hot, or when it's cold too?

It could be the temp relief valve, could be the springs on the pressure relief valve have become weakened.

I would start by checking one cylinder. (the most prolific water looser!)

I would see if it leaks cold. Running outlets, and ubruptly shutting them. Then I would warm the unit up, and take a temp reading on the closest hotwater outlet - make sure it's not over 70.

With the cylinder hot, I would then repeat step one and run taps, and ubruptly stop them.

If this causes it to spurt at the tundish, I would reinstate the air bubble. (You must not open any hot outlets while doing this, or you won't produce the right air bubble). I would also shut the water off and take a reading of the pressure after the Pressure Reducing Valve). If it's over 2.8bar you know you have issues.

Then I would change the Pressure relief valve and the combined Pressure/temp relief valve. Then run all the tests again.

If the problem still persists, after you have checked pressure, valves, temps, and reinstated the air bubble. I would then fit an additional white expansion vessel.

This sounds like a lot of work, and I guess it is. It will take a guy about half a day messing around. But if you nail the problem, it will be time well spent, and the others will be easy to fix.

 

[musgrove]

You could fit an external expansion vessel (white ones for hot water).

Thanks very much for your suggestions. The lime mortar pointing is being washed out by constant soaking with hot water, plus cracked window panes etc. I am not a plumber, but i thought the air pocket was the expansion vessel? It is an unvented cylinder.

 

[tamz]

The air pocket does take the place of the expansion vessel but sometimes needs replenishing frequently.
They are a pita to be honest.

 

[musgrove]

Overflow????
dont you mean the blow offs are passing water on the megaflow as its unvented!!

Thanks, guys. I have pretty much already done everything you suggest, short of fitting an additional expansion vessel. The pressure is less than 3 bar, the temp is less than 70, none of them leak cold, have replaced thermal/pressure relief valve, regenerated through drain cock, etc etc. I am concentrating all my efforts on the worst culprit as suggested. The frustrating thing is, some of them have no N/R valve, stop leaking when you regenerate the air pocket and generally behave. Have swapped off peak and booster feeds to immersion heaters, so I can see what is happening during the night in daytime tomorrow. Will let you know how it goes... Thanks again for all the helpful comments, much appreciated!

 

[justlead1]

Is it time the termination of discharge pipes on unvented is revisited? With the cold winters we are experiencing and high level discharge pipes, freezing becomes an issue. When tundishes overflow within the honeycomb type flats we now build. The damage is not confined to the property/appliance at fault.

 

[gassafe]

I would try turning off the immersion heaters to one of em... see if it stops discharging when tank is full of cold water!
It could be the TPRV valve on the tank is all scaled up and not even sealing properly anymore...
I wudent have thought they wud need another expansion vessel, i thought these were sized up accordingly!!
I had a similar job to this once, it only needed the cyl stat tweeking down to approx 50-55 if its low down on the tank =]

 

[musgrove]

Think I have found the answer. (To be honest, it was my mate John!)
We found that many of these tanks have not got an air pocket, even if regenerated in accordance with HS instructions. To check, turn off mains stopcock, turn on a (low) hot tap. Water equivalent to the size of the existing air pocket will run out. It should be about a 1/4 of the volume of the tank. If you only get a few litres, the air pocket needs recharging. Some of them do not get enough syphon effect just by opening a tap. What we did was:
1) Remove a shower head, lay hose down in tray, and connect 3/4 BSPM to hose fitting. Fit 10m of hose, and chuck out of nearest window.
2) Turn shower to max hot
3) Open T/P relief valve.
4) Close stopcock.
5) Wait until water stops running out of hose. This will be when water level in tank drops below hot water outlet pipe.
6) Close shower valve
7)Close T/P relief valve.
8) Open lowest hot tap in system
9) Open stopcock
10) Close hot tap.

If there is still a problem, it is probably becuse the TP relief valve seating is scaled up. I'll let you know if it works in a month or so.

 

[plumberdarren]

Be careful as you should have an Unvented certificate so shouldn't be working on them! (you already stated you weren't a plumber?)

 

[musgrove]

You may well be right Dazzer, but in that case why do HS put a big sticker on the tank telling you that you must regenerate the air pocket regularly and tell you how to do it? BTW, it is a stand alone unit, and not connected to a boiler.

 

[plumberdarren]

Regenerating the air pocket is fine but other mechanical stuff has to be done with certification.

 

[Dannypipe]

That's true. Its simply that in the wrong hands these can be dangerous.

Example: Unqualified installer fits one, and chucks the tundish in the bin. Months/years later someone spots water dribbling outside via the discharge pipe. They go down B & Q and buy a speed fit stop end. Stuff it on the end, and no more dribbles....until BANG.

It's happened.