I want to improve my gravity fed hot water by adding a pump

[simonaoz]

I want to add another pump to pump the hot water from the boiler around the coil in the hot water cylinder to improve efficiency. At the moment the boiler has two circuits, one gravity feed to the hot water cylinder and one pumped (on the return to the radiators).

1. Can I add a pump next to the cylinder?
2. Is the pump best on the flow (top connection) or return (bottom connection)?
3. Should I fit a two port valve to stop syphoning?

Thanks for your help.

 

[kittedup]

Why don't you just convert to Y plan or S plan. Only one pump needed then.

Ted

 

[simonaoz]

The layout would make it tricky. The boiler has 4 tappings and is in the garage, and the rad circuit is via a manifold with a pump on the return. F&E feed is at to tee at bottom of cylinder coil and vent is at tee at the top of the coil. So I was hoping the addition of a motor valve on the feed to the coil after the tee and a pump on the return from the coil ( next to the cylinder ) would make things more efficient. What do you think - I'm not sure if this would draw air in or over pump in to the F&E cistern.

 

[hym]

1..no
2..no
3..no
You need to update to fully pumped and why not consider updating boiler as well as it is probably a cast iron heat exchanger very inefficient and probably qualify's for scrappage scheme.

 

[kittedup]

You could always add the 2 port onto the return from the cylinder which will help with efficiency.

Ted

 

[simonaoz]

Thanks Ted, I'll put a two port in and that will give me individual ( zoned ) control of the hot water, but what do you think about a pump to decrease the reheat time?

 

[twgas]

Adding a pump with no consideration to the pipework will lead to trouble, pumping over and/or air ingress.

 

[simonaoz]

Thanks for all the comments and help. I think I will just add a two port valve for now and change to S plan if and when the boiler gets changed.

 

[JohnD]

I added a pump, cyl stat and 2-port valve to my old mum's Gravity HW system and yes, it did tend to pump-over momentarily if the HW pump cut in when the CH pump was already running. Also it caused slight parasitic circulation on the CH circuit when only the HW pump was running. The pumping-over was cured by putting the HW pump on its lowest setting and constricting it with the gate pump valve. The system now reheats the cylinder much more quickly and is a lot more economical in summer as the boiler is not constantly cycling and the HW Primary circuit pipes are not constantly hot and losing heat warming the landing floor.

But I agree a 3-port would have been a better way to do it. Like you I was put off by the difficulty of repiping 28mm in a constricted area (boiler room was built around the boiler after installation). I am not skilled at pipework and the method I used was quicker and easier for me.

28mm motorised valves are particularly expensive and I happened to have a 28mm 2-port.

You need to change the programmer setting from Gravity to Pumped, and change the wiring for the controls, this is fairly easy following the instructions using a Wiring Centre.

 

[D_Hailsham]

Thanks for all the comments and help. I think I will just add a two port valve for now and change to S plan if and when the boiler gets changed.

Here is the wiring diagram for the C Plan. One advantage of this plan is that you can have separate CH and HW times; no longer restricted to HW always ON when CH is ON. If your programmer is set to gravity, you can set it to pumped.

View media item 73

 

[simonaoz]

New tank in with the addition of a two port valve. Hopefully get it all wired up tomorrow. Thanks for the wiring diagram D_Hailsham. I was thinking I would have to use a relay, but that will work just great.

 

[IKM]

After reading the positive comments above from JohnD I decided to add a pump to the DHW cylinder primary return on my C-Plan system to improve the hot water recovery time. This became necessary after fitting a power shower. The pump was fitted between the primary return connection to the cylinder and the 2 port control valve. The live wire from the pump was connected to the cylinder stat output, terminal 8 in the wiring centre. I used a 5m head pump and set the output to minimum. I was careful to check that pump position did not obstruct the feed or expansion pipes to the boiler.

Installation was relatively easy even with 28mm pipes and restricted access. The time and cost to convert to a Y or S Plan would have been prohibitive.

The improvement in performance is amazing. There is always sufficient hot water for showering even with up to 6 people using the shower over a few hours and with the central heating operating at the same time. There have been no problems in the 6 months since installation.

 

[simonaoz]

A year after fitting the zone valve my oil consumption was down 4% on 2009 and 9% on 2008. Recovery time is about 1/2 hour.

 

[Tipper]

I did this too about 6 years ago and it was a great success.

I already had a zone valve on the gravity return from the cylinder to control water temperature but recovery time was slow due to long horizontal pipe runs. I added a return pump next to the valve, down by the boiler, and used the auxiliary contacts on the valve to start and stop the pump automatically. Position of the vent/feed was not compromised.

And yes before you say it's a bodge, it is, but it works well particulalrly when the existing system works and re-designing and re-installing a more modern system would be very costly and disruptive.

(No way I was going to suffer the wrath of SWMBO by lifting newly fitted carpets for a 'bit of plumbing'!)

 

[Fastlearner]

I have a Glow-worm back boiler unit which is tapped for graviyy feed by 4 connections.The central heating has a twin pipe flow system and separate return.I believe this comlex set up is because of the shape of the bungalow & the remote location of the pump (15 mtrs.from boiler).It works extremely well & the boiler is bullet proof.The hot cylinder( roof space) is compromised & needs replacing.At this point, sourcing a gravity cylinder is difficult as most suppliers only stock units for pumped systems.I am unwilling to upgrade a complex but very effective system just because of a defective cylinder.
I like the idea of a 2-port valve & 2nd pump on the return side of the heating coil & controlled by a cylinder stat as suggested by JohnD.
Do i need to fit a 2nd programmer to control this set up so that it works independantly of the central heating pump.

Ron