Secondary return on cylinder

[leiadad]

Hi was looking for bit of help with secon day pump. Was asked to replace a secondart pump the other day in a hotel which I done. After fitting the new pump when the pump is flowing the pressure decreases quite considerably, the pressure drops even more depending on which speed the pump is set at, I can't remember how it's working whether if you drop from speed 3 to speed one the pressure gets higher or lower and vise-versa. It gets to a point that the pressure loss at taps results in no water coming out at all. The cylinder is feedin one floor. I have had to switch pump off at moment as pressure is ok without it on at moment. Only thing I can think of is it is ducking too much water through circuit and not getting a chance at branches. Any help would be appreciated

 

[ShaunCorbs]

How's it teed into the cylinder?

 

[leiadad]

Into boss at high level if o can remember right

 

[leiadad]

Sorry kept having typo errors

 

[snowhead]

Is the water circulating, both the flow and return are hot around the system?

If not, is the valve on the flow open?

 

[ShaunCorbs]

Into boss at high level if o can remember right

Into the cylinder?

 

[leiadad]

Yes into cylinder it's a secondary hot, so water is always hot at each branch

 

[ShaunCorbs]

Yes into cylinder it's a secondary hot, so water is always hot at each branch

Unvented or gravity cylinder

 

[steadyon]

Hate to ask, but is it pumping the in the right direction, i.e. with the arrow on the body of the pump pointing to the secondary return inlet at the cylinder?

 

[leiadad]

It's gravity shaun

 

[leiadad]

Yes steady on its pumping in towards cylinder

 

[leiadad]

Tanks only about 10 metres above but can't think if that would cause any problems. I'm just wondering if the system has never worked right and they have maybe oversized the circuit causing it to just run round that circuit all the time

 

[leiadad]

What you thinking shaun when you ask about it being unvented or gravity

 

[leiadad]

I'm also pretty sure it has no check valve on but assume this is only necessary when pump is not on to prevent hot water going up return leg rather than through hot side

 

[ShaunCorbs]

What you thinking shaun when you ask about it being unvented or gravity

It's not pumping over is it when the pumps on ?

 

[leiadad]

I didn't check, but I am back on Monday so will have a look. What would this suggest shaun. Would it be that it is pumping back up the cylinder and finding an easier route up the vent. If so how would you prevent this if that was the case

 

[leiadad]

The pump that was fitted is a bronze pump for secondary so it is correct pump for the job

 

[ShaunCorbs]

The pump that was fitted is a bronze pump for secondary so it is correct pump for the job

Correct size ?

 

[ShaunCorbs]

I didn't check, but I am back on Monday so will have a look. What would this suggest shaun. Would it be that it is pumping back up the cylinder and finding an easier route up the vent. If so how would you prevent this if that was the case

And lower the pump setting / speed / spec a different pump doesn't need much only need a trickle

 

[leiadad]

Ok thanks for the help

 

[Monsanto]

First of all I am not a qualified plumber! However, if this pump was on the flow would that not solve the problem?

 

[leiadad]

It's not on the heating. It's a seconday pump

 

[Monsanto]

I am sorry, maybe I misunderstood the application. I assumed this pump was to circulate hot water in a loop, from and back to the hot water cylinder, with take off points to hot taps at different locations. The aim being to shorten the time to get hot water to the taps. When I have done this I sited the pump on the pipe coming from the top of cylinder (flowing away from cylinder), before any branch pipes, with the "return pipe" going back to the cylinder lower down.

 

[ShaunCorbs]

I am sorry, maybe I misunderstood the application. I assumed this pump was to circulate hot water in a loop, from and back to the hot water cylinder, with take off points to hot taps at different locations. The aim being to shorten the time to get hot water to the taps. When I have done this I sited the pump on the pipe coming from the top of cylinder (flowing away from cylinder), before any branch pipes, with the "return pipe" going back to the cylinder lower down.

You've fitted the pump wrong then

 

[leiadad]

I have never seen a pump fitted the way you are saying Monsanto. I am not sure of the effects that this would have on the circuit. I am assuming it will duck air in from vent as it will be under quite strong negative pressure

 

[dan_the_plumber]

Should be a bronze pump on the return. I’d suspect the pump has been fitted backwards.
However as a different idea, what about if the ‘flow’ and return have got different flow rates. We’re talking now about pipe sizing and number of bends ‘equivalent pipe length’.
If say we are pumping out in 15mm and the return is in 22mm then the volume of water in the DHW pipework will decrease and so the pressure will drop

 

[leiadad]

The hot coming off the cylinder is in 22 and the pump is 100 percent feeding in the correct direction. It's a bronze pump

 

[dan_the_plumber]

The hot coming off the cylinder is in 22 and the pump is 100 percent feeding in the correct direction. It's a bronze pump

Ok fair enough, maybe there’s a valve closed/part closed on the secondary run?