Problems with secondary return pump. Pulling my hair out!!!

[Plucky]

Hi all.

I am having problems with a secondary hw pump I have installed. Basically it's not circulating. It sounds as if at has air in it or pumping against a closed circuit.

I have vented the pump via the vent screw and no air. There are valves on the hot water distribution pipe as it splits into 2 (no valve on vent) and if I shut these down and open hot taps I get hot drawing back via the secondary tapping so this proves there is flow through the pump and that there are no hidden valves that are shut on the return leg.

So why can I not get circulation? I have not fitted a non return valve but I can not see this to be a problem. The pump is a grundfos 15-50 bronze, the right pump for the job. The hot water distribution pipe is 28mm and return 22mm so it should fly round!

Thanks

 

[unguided1]

sounds like it might be air locking somewhere

 

[Plucky]

I would agree but I am able to draw water through both the secondary return leg and the hot dist pipe. This would prove no air lock. I am able to isolate various pipes to ensure that the HW isnt creeping through another way if that makes sense.

 

[unguided1]

You say that you have a 28mm feed and a 22 secondary I assume that this is a commercial installation how high is the building and how far is the secondary return pump from the return tapping

 

[Plucky]

Its not commercial just a big house. The pump is about 3 feet from the return tapping. I have to go back there later for something else. I shall take some pics.

 

[Plucky]

Do you think it matters that there is no non return valve fitted?

 

[unguided1]

I would always put a non return valve on a secondary return. I also always put a timer on to the pump or wire in a pipe stat as it does not need to be circulating all the the time only just before typical peek times.
Also up to 28mm i would also say you only needed a 15mm secondary and make sure its all insulated.

 

[Plucky]

I have wired it into a single channel time clock. I did not fit the secondary circuit. It is about 30/35 years old at a guess. There was aready a pump which I have replaced when I replaced cylinder. The old pump was burnt out and looked ancient!

 

[unguided1]

Hi Plucky

Looks like you have found a proper nightmare then, have you been able to trace all the secondary return pipework because this still sounds like an airlock, mind you saying that installers back then really understood the concept of airlocks and installed their pipework to suite. I have thrown lump hammers at apprentices who have tried to tell me it doesnt matter about airlocks on a pumped system. By the way I am not infering that you are either an apprentice or that you do not know what your doing.

Have you checked to see if the tapping in the cylinder is clear I have had problems in the past with limescale building up on the hot water outlet at the top of the cylinder and in the secondary return tapping.

 

[gaspastemania]

Pump valves open?
impellor is spinning?
just couple thoughts

 

[ecowarm]

have you checked the system because old systems like this used to have towel radiators installed on the secondary cirulation and may need venting

 

[coley]

what position is the pump in?

 

[coley]

the new way of doing according to grundfos is to place the se pump in the sec pipe pumping away from the storage tank.
so when all outlets are closed the hw circulates back to the storage

 

[ecowarm]

same as if in the return surely?

 

[coley]

the pump is better in vertical pumping upwards if it is tank ferd and by the sounds of it, it is.

 

[ecowarm]

I was always told a pump is better pumping down

 

[kimbo]

I heard from more than one source that there was a problem with this happening and it was burning out pumps so grundfoss advised to turn pump around so it pumped other way. It cured the problem, its worth a try I have never tried it myself as the dragons say its worth a punt.

 

[justlead1]

Hi. Before you go to far. isolate the pump and change to another pump (any pump) as it may well be that the pump is not working as is should. Trying a pump that you know works, will help to identify the problem. You can also valve the hot draw off, isolate it and with the pump off check that water can be drawn via secondary return. This should give you an idea of whats playing up. Good Luck

 

[Plucky]

Thanks for the pointers.

There are no towel rads on the circuit. The impeller is spinning. The pump valves a open.

The secondary tapping is clear because if I shut the valves off on the normal distribution pipe and open hot outlets anywhere in the house the water flows to the taps through the pump through the secondary leg.

I think I could try turning the pump around but seems to go against everything I was taught, and I have never had a problem before. I have probably installed over 100 secondary HW systems, admittadly 80% have been on unvented systems.

Il post some pics in a bit

 

[coley]

is the pump noisy ie ratling

 

[hot stuff]

i have had this prob before and have turned pump around and it has worked worth a go.good luck

 

[kimbo]

Just done the same today works a treat