hot water pushing its way into the header tank through the feed to the calorifier

[liddywolves]

Hi i am currently having problems with a system at work, it is 3 storey block of flats where there is 2 header tanks in the loft and 2 steam fed hot water storage calorifiers down in the basement, hot water is forcing its way up the feed pipe and into the header tanks, i tried running on 1 tank and only 1 calorifier and swapped them about a bit to see if it would help, but it didnt, i have recently taken 1 out due to insurance inspection in a bid to see if the coil was burst but this wasnt the case, the only thing i am resulting in doing is putting a non return valve on the feed, but this is only going to force the problem elsewhere, i cant have the hot water feeding into the header tank with legionella regulations, any suggestions???
thanks

 

[justlead1]

Hi. It is quite normal for the water in calorifier to expand on heating and displaced water to pass up cold feed. If a non return valve is fitted the expanded water will discharge into cistern via vent. This can be proven by turning off the gate valve on the cold feed, prior to heating water. (providing none is trying to be drawn off.) Do the legionella regulations state to temperatures to be avoided? Are you achieving this? I think it is 20 to 45 degrees that it grows and 36 it likes best.

 

[steadyon]

You might also want to check if there are any mixer taps / mixer showers or thermostatic mixing valves on the system. I have known these have their non return valves fail, resulting in the high pressure mains forcing hot water back into the cold water storage cisterns. Should lead to constantly running warning / overflow pipe, unless sufficient water is being drawn from the tanks to stop the overflow.

 

[liddywolves]

Hi. It is quite normal for the water in calorifier to expand on heating and displaced water to pass up cold feed. If a non return valve is fitted the expanded water will discharge into cistern via vent. This can be proven by turning off the gate valve on the cold feed, prior to heating water. (providing none is trying to be drawn off.) Do the legionella regulations state to temperatures to be avoided? Are you achieving this? I think it is 20 to 45 degrees that it grows and 36 it likes best.

Regulations state that it must be under 20 degrees, often the tank is up in the 40`s, and has to be drawn off via sinks and baths to get the temperature down below 20 again, i need a solution in why this problem has suddenly occured, the water board will start to think we have a leak with the tank being drained every day.

 

[justlead1]

Hi. If a large system as the post suggests. Is a secondary return employed?
A pump on this side of the system can create this situation under certain conditions. Or that which has been suggested, some one has fitted a mixer or mixer hose, creating back flow when in use.

 

[liddywolves]

Hi. If a large system as the post suggests. Is a secondary return employed?
A pump on this side of the system can create this situation under certain conditions. Or that which has been suggested, some one has fitted a mixer or mixer hose, creating back flow when in use.

yes there is a pump drawing the water on the return system back to the calorifier, the building is very large and full of thermostatic mixing valves on near enough on every sink bath and shower. cold water is drawn of the mains, would 1 mixing valve at 15mm size diameter of pipe cause this much pressure to push hot water up 3 levels against gravity from the header tank. i have tried knocking parts of the building off to see wheather or not i can point the mixer in a certain area but this has failed.

 

[justlead1]

Hi. The shower mixers have non return valves in (in quality units) Mains pressure will back up 10 metere for every bar of pressure. You may well have 4 or 5 bar at mains. Its well worth investigating as nrv's do malfunction. Have any of the flats had work done on the system lately? Needles can be found in haystacks, it just a question of time. Good Luck

 

[liddywolves]

Hi. The shower mixers have non return valves in (in quality units) Mains pressure will back up 10 metere for every bar of pressure. You may well have 4 or 5 bar at mains. Its well worth investigating as nrv's do malfunction. Have any of the flats had work done on the system lately? Needles can be found in haystacks, it just a question of time. Good Luck

yes there are constant works carried out on these flats with refurbishments with it bein accomodation for nurses and doctors at the local hospital, we have 7 bar of mains pressure, so for each tmv that is not working it will back up 70metre??? crikey that will sure to push it up 3 floors.

 

[justlead1]

Hi. I may be time to implement some form of terms/specification, and inspection for whose wishing to refurbish plumbing systems within the building. Being medical they are sure to know the problems associated with storing warm water. The fact you will have to check it out when nurses are showering could get you into trouble. Good Luck

 

[Rodreguez]

i work at a hospital on the exact sort of systems you're on about. The legionella regs on calorifiers state there should be a NRV on the cold feed and DHW return within 300mm of the calorifier. i've had a lot of work updating systems to the new regs! Does the calorifier has an anti-legionella/de-stratification pump? If so how is this set up? Does it run constant or timed? The minimum is 1 hour per day. If it is constantly running this will cause the whole calorifier to remain at a constant temp throughout. this could cause hot water to rise through gravity up the cold feed. but depends if the cold feed is a straight pipe from tanks.

I have also had alot of probs with thermostatic mixing valves letting by and mainly blowing hot up the cold pipework. this can be time consuming to trace.

 

[liddywolves]

Hi. I may be time to implement some form of terms/specification, and inspection for whose wishing to refurbish plumbing systems within the building. Being medical they are sure to know the problems associated with storing warm water. The fact you will have to check it out when nurses are showering could get you into trouble. Good Luck

hmmmmmmmm haha

i work at a hospital on the exact sort of systems you're on about. The legionella regs on calorifiers state there should be a NRV on the cold feed and DHW return within 300mm of the calorifier. i've had a lot of work updating systems to the new regs! Does the calorifier has an anti-legionella/de-stratification pump? If so how is this set up? Does it run constant or timed? The minimum is 1 hour per day. If it is constantly running this will cause the whole calorifier to remain at a constant temp throughout. this could cause hot water to rise through gravity up the cold feed. but depends if the cold feed is a straight pipe from tanks.

I have also had alot of probs with thermostatic mixing valves letting by and mainly blowing hot up the cold pipework. this can be time consuming to trace.

yeh i have seen this regulation about the NRV, but our system is 50 year old has been in since day 1 from when the building was built, there is no destrat pump, and the pipe is vertically down 3 floors then horizontal in the ducts to the calorifier about 15 metres. if a non return valve is fitted will this not send the problem elsewhere?

the calorifier is steam fed with a hair pin coil, and is drawn by a return pump round the building, when feeling the feed pipe from the tank after being drained you can feel the pipe warming up until finally reaching the tank and sending the tank up to as high as forty degrees when left over night!!!!