overflow from cylinder

[Neil T]

Just been to look at a overflow problem at kids day care centre. The c/w cistern kept filling to point of overflow. I checked valve and replaced washer and float as both were looking dated. Dropped water level and left it for a few hours. Went back and level is back up and overflowing again. As its a commercial building there it resembles spaghetti junction with pipework everywhere you look and I've only done domestic before so it was a bit daunting to say the least.
After scrambling around in roofspace I managed to track all pipework and went to boiler room to refind them there. Vent goes into dhw cylinder and thermostat reads 55 degrees so no immersion prob. Although checking pipework from cylinder, there is a secondary pump which is wrong way round (arrow against flow). Gut feeling tells me that when this kicks in it forcing hw back into cylinder and out of vent, am i right? I can see why it's actually been done like that, but it's pure laziness. The elec socket is in way of elec terminal on pump and it would have to be facing away so you cant see pump face. There are arrows all over every pipe indicating flow too so i dont see it as accidental.
Everything else seems ok with system. Pressures are slightly up but not by much.
its a big system with 2 ch boilers and 1 dhw boiler. The council used to run and service building but now its private they won't touch the place. It's due for service in may but its too bigger job for me and I havent got gas quals anyway. (Job hanging there for someone lol)
I'm going to place pump right way round tomorrow to see if that solves problem. Any other thoughts?

 

[snowhead]

Any TMV's with tank fed hot and mains cold?

 

[BLOD]

Which way is the pump pumping, towards or away from the hwc ? Try leaving the pump switched off and see if the cistern overflows then.
I'd also be checking for backfilling via mixer taps and showers etc and maybe a split hwc coil.

 

[Neil T]

Snowhead - i presume there would be some as its a nursery and was council owned but haven't had a proper look around the place. There are showers there too. They are only using part of the building at the moment as they only took it over towards end of last year and they say its a new problem. I asked one of staff to run all hw taps inc showers while I was up checking float valve in cistern and there was a little air in a couple of taps but nothing major.
Blod - the pump is pumping towards cylinder on pipe that flows from cylinder. The showers don't get used yet and they only use one classroom with sinks, toilets and kitchen all of which don't have mixer taps. They say it always happens in morning when they get there are intermittent during day.

 

[BLOD]

the pump sounds like its pumping the right way for a secondary return.
Can you isolate the supply to the shower valves ?

 

[Neil T]

The pipework has arrows pointing away from cylinder and pump arrow points towards cylinder?
I presume there are iso valves and I hope they are near showers cos its a maze of pipework in the roof space and in boiler room. As i said earlier im only used to domestic systems and this is big! I know its basically the same as a domestic system but on a far larger scale, but tracking where pipes go and all the extra pumps, valves etc made me go 'Eeek!' or words to that affect

 

[AtlasGas]

Agree with snowhead, non returns are passing on TMV's

 

[Neil T]

I'm due there tomorrow at 1pm but I'll go in morning and turn off secondary pump and see if anything happens between me returning in afternoon. I'll then Isolate showers as they arent being used anyway and check tm valves.

 

[Neil T]

Update: called this morning and isolated the secondary pump and marked water level. Been nearly 3 hrs and no rise in level. Checked building for tmv's and mixer taps found 4 tmv, 2 shower mixers and 1 basin mixer (which has cold feed isolated and runs luke warm) showers aren't actually standing showers but in large basin or sluice for washing dirty kids I believe.
Going to reconnect pump and give it an hour to check level again. If no difference then will isolate all tmvs and check level on monday morning as can't get access till then. If still no change then will isolate shower mixers for a few hrs and check level again.
After that ...?

 

[Neil T]

Oh I can't find tmvs for the kiddies basins either which I found unusual. I know there should be some unless they are concealed or in roof space.

 

[albatross]

Coil in cylinder may have a pinhole in it.

 

[Neil T]

Just trying to see if water is coming in from cylinder or back filling through cold outlet. Reconnected pump and sat in loft with a brew (but no bics!) waiting to see if any difference in level. Been to look at cylinder again and its a biggy. Changing that wont be a quick job, especially draining this system. Job may be too big for me but don't like walking away, no surrender!
Going back to the pump. I was taught to go with flow concerning arrow on pump, however no one has commented on that. Is it not an issue?

 

[albatross]

secondary circ pumps are usually on the return loop, pushing back into the cylinder on a low speed.

 

[Andyswad]

Coil in cylinder may have a pinhole in it.

If it has and the heating feed expansion tank is above the cw cistern the water will try to find the same level.

 

[snowhead]

Going back to the pump. I was taught to go with flow concerning arrow on pump, however no one has commented on that. Is it not an issue?

Have you checked the true direction of flow in the pipe or just relied on the markings, as it's not unusual to find the arrows the wrong way, sometimes you can follow arrows and meet some on the same pipe pointing back at you.

 

[Neil T]

Cheers lads. The bloody arrow on pipe was wrong!! Sat in loft for an hour watching water level after reconnected pump and found that its slow back flow into cistern through cold outlet and not from hw cylinder vent. Ive isolated all tmv's that I could find (except ones in classroom that they use and another that had no iso valves anywhere near it) Also couldnt isolate showers as they have no iso valves either. I marked the water level and going back monday morning as I've no access over w/end.

 

[BLOD]

sorry - forgot to say you could have just turned the mains off
hope the loft was nice :39:

sounds like you might have a result !

 

[Neil T]

Cheers, next time I'll take some biscuits

 

[Neil T]

Went back next day to find it overflowing again so isolated tmv to basins in last classroom and the shower in there. Sat in loft for another hour and watched water level and there was no change. So capped off shower as they don't need it and problem solved. Thanks for input lads

 

[BLOD]

good result - glad you got it sorted