Convert gravity system to fully pumped

[Bob Croft]

My customer has requested that thier CH / DHW system be converted to fully pumped because the DHW is slow to heat up.
The system consists of pumped CH with the pump located in the boiler casing (GW Hideaway 70 BF) the CH pipes go under the floor.
THE DHW cylinder is fed by 22 mm pipes (should be 28) with a vertical run above the boiler of 2 metre and then a horizontal run of about 8 metre with several bends for each pipe. Both the FE and vent pipes are 15 mm and are connected close to the cylinder, FE to return and vent to flow. Thus the FE and vent are remote to the boiler. The cylinder is located in the attic.
My proposed solution is to install a second pump in the DHW flow pipe with close coupled FE / vent via an AirJec just prior to the pump. This pump would be controlled by a cylinder stat and programmer. The FE tank would be about 2 metre above the pump. I would increase the vent pipe to 22 mm.
This approach seems easier than implementing a S or Y plan and having to move the FE and vent pipes close to the boiler. Does anyone have any experience of doing a similar conversion or can see any problems / issues with my proposal.
Thank you.

[migoplumber]

have you referred to the manufacturers instructions for a schematic. they will be able to give you better information than me, and you will know its 100% correct?

failing that your idea sounds about right!


shaun

[Bob Croft]

Shaun, I have referred to the manufacturers manual. The existing set up is as per the diagram in the manual except for pipe sizes. The set up for a fully pumped system is the usual pump + MV with the F/E and vent connected to the boiler. The purpose of my post was to enquire if other people had any experience of twin pump systems. I understand that these were popular some years ago and presumably used with the older cast iron boilers such as the one on the installation I am working on.
Many thanks for your reply and for the other very interesting posts you provide to other enquirers.

[puddle]

The problem with a two pump system you mention is that the two pumps can fight each other and one will be burnt out
Thats why when two pumps are used like you mention on older systems,mostly commercial,belt operatated pumps were used,taking stress from motor and putting on replacable belt

[migoplumber]

you can install as many pumps as you like on a system, so long as its designed well, incorporating the correct valves, and pipe sizes, and switch controls.

if you go to an installation and find pipework, with more than 1 pump, with pumps fighting each other its because it has been badly designed or installed!!

done a couple of installations myself, where ive forgotten a NRV or AAV and as a result caused myself a return visit. dosnt feel good when you walk into your own plant room, commenting what a plonker ive been, if only i'd seen that before !!

havnt been any for years tho. must point out.

shaun

[puddle]

Are you saying the system in question is
'designed well, incorporating the correct valves, and pipe sizes, and switch controls.'
to allow two pumps to be fitted,if I thought it was ,no problem,but I do'nt and think that there is a possibility of one pump being burnt out by the other,although the flows for heating and hot water are seperate
,the cast iron heat exchanger on the hide away is not very big and the pumps will fight each other,which if you contact golw worm they will confirm
Also it is not doing the customer any favours as when the time comes to replace the boiler the system will still require up dating correctly,with zone valve/valves making second pump work wastefull

[migoplumber]

no, not at all puddle. soz, ive either said it wrong or its been misintrepeted. i apologise for that.
mine was a generalisation.

the system in question i cant quote perfectly because i have not seen it, or schematics for it, for that reason i was trying to "generalise"

i did not mean to be little your comment, only make a general point.

shaun

[puddle]

Sorry migoplumber.I was trying to reiterate a point by quoting you,trying to save time however upon reflection,I appear to have taken your point out of context and ended up making your statement look incorrect which obviously it is not,I should have taken more time checking the reply,sorry again
However Bob I do think you could have a problem with two pumps on this system