Can I reverse my CH/HW Pump

[Shovelhead666]

Hi, might seem an odd question but can a central heating pump be reversed.

Pump has never been housed in the Airing Cupboard. Normally located after the expansion overflow and the 3 way valve.

Pump has always been located where the boiler is.

Noticed that the pump was not directed towards the 3 way valve and was actually pointing the opposite. circulating to the radiators and the hotwater tank then to the 3 way valve. Swapped it round and now I'm getting water flowing out of the expansion overflow. (Not the HW tank)

Can a fully pumped vented system work the opposite way based on the pump having to be located near the boiler.

Can a 3 way valve work the opposite way round ?

Thanks for any advice

 

[Exedon]

Some clear pictures of boiler pump 3 port and pipework would be useful.
Is pump on return by any chance?

 

[Shovelhead666]

Hi, thanks for the quick reply. I'll get pictures when I get home. Yes it's on the return feed

 

[fixitflav]

Hi, thanks for the quick reply. I'll get pictures when I get home. Yes it's on the return feed

A hand sketch showing relative positions of the various bits could be more useful.

 

[Shovelhead666]

On the schematic the drawing on the right is the way my system is set up. The one on the left is how it should be but the motor in my system has never been between the expansion overflow and the three way valve. It's always been on the return of the boiler.
Thanks in advance for any guidance.
The three way valve is a Honeywell

 

[fixitflav]

On the schematic the drawing on the right is the way my system is set up.

I can't see any reason why that wouldn't work. The pump is more often on the boiler flow, but some claim advantage of it on the return, as the pump runs cooler. If you're getting pumpover, most likely reason is partial blockage between the open vent and cold fill connections. Could there be some sludge in the system?

Can a 3 way valve work the opposite way round ?

The valve sees the same conditions in both your arrangements - flow into leg of tee, out of port A and/or port B.

 

[Shovelhead666]

I can't see any reason why that wouldn't work. The pump is more often on the boiler flow, but some claim advantage of it on the return, as the pump runs cooler. If you're getting pumpover, most likely reason is partial blockage between the open vent and cold fill connections. Could there be some sludge in the system?

The valve sees the same conditions in both your arrangements - flow into leg of tee, out of port A and/or port B.

Hi, yes this is the current set up.

The way I look at it the pump draws away from the expansion overflow in the first diagram but the second diagram (My current set up) it pushes to the expansion overflow.

My question is if I was to reverse the pump so the flow runs to the rads, hot water coils then to the 3 way valve would it be an issue.

Will the three way valve work in reverse

Thanks, Jim.

 

[Shovelhead666]

For the record the system is completely clear. No sludge in the tank all pipework flushed out

 

[fixitflav]

The way I look at it the pump draws away from the expansion overflow in the first diagram but the second diagram (My current set up) it pushes to the expansion overflow.

The pressure at the cold feed connection is constant, determined by the height of the F/E tank. In diagram 1 that's the minimum pressure at any point, maximum after the pump. That's the preferred setup.
In diagram 2 the minimum pressure is lower, being the cold feed pressure minus the headloss through the rads. You don't want it to drop below atmospheric or there's a risk of drawing air in, but I doubt that would be the case with your setup, that's why I said I think it's OK. (if you want to find the actual pressure at any point you need to take account of the level)

My question is if I was to reverse the pump so the flow runs to the rads, hot water coils then to the 3 way valve would it be an issue.

Why would you want to do that? If you did, you would need to swap the boiler flow and return.

Will the three way valve work in reverse

I doubt it. There will be a differential pressure pushing the ball off its seat, so may not seal too well

 

[Shovelhead666]

Hi again, I took a further look at the existing system and it is different to my original draft. Turns out the feed from the expansion tank goes to the bottom of the hot water cylinder coil outlet.
It would be quite straightforward to change this and attach this direct to the boiler feed just before the 3 way valve. Like in the diagram I originally posted. For clarification I've included another schematic of current set up and the proposed.
Thanks for all your feedback so far fixitflav

 

[fixitflav]

Hi again, I took a further look at the existing system and it is different to my original draft. Turns out the feed from the expansion tank goes to the bottom of the hot water cylinder coil outlet.
It would be quite straightforward to change this and attach this direct to the boiler feed just before the 3 way valve. Like in the diagram I originally posted. For clarification I've included another schematic of current set up and the proposed.

That should be an improvement. The way it's set up now explains your pumping over, as the pressure into the vent pipe is increased by an amount equal to the boiler headloss.
Don't forget to make your new cold feed up-and-under, to reduce convection warming of the F/E tank and encouraging algae growth

 

[Shovelhead666]

Awesome, will get on it next weekend.
Thanks for all the advice and support

 

[fixitflav]

Awesome, will get on it next weekend.
Thanks for all the advice and support

Did it go OK? How's it working?

 

[Shovelhead666]

Hi, busy at the weekend didn't have chance. Hopefully get done this Sunday.
Just curious but do you think I could do the convection turn on the boiler feed side ?

 

[fixitflav]

Just curious but do you think I could do the convection turn on the boiler feed side ?

Not sure what you mean. Please explain