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Replacing DHW primary circulating pump

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Philip Saunders

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Hi everyone

I have a dead pump on my DHW

This monster pushes water around the heating coil of s 210 litre unvented cylinder. That's all

It used to be 2 cylinders, and will be again at some point (I have questions about that too but I'll create a new thread)

My question is - does anyone know if this pump can be rebuilt? If not - can anyone suggest a replacement? Best I can do so far costs over £1000, which is bonkers when I know a domestic circulator would do the job - problem is I can't fit one to 2.5 inch iron pipe and 3 phase supply.

Suggestions anyone?

I did ask over on the electrician forum about changing the supply to single phase - that's not simple either.

IMG_20190322_145552.jpg
 
do you know the loop length? eg the circuit length

and anything can be rebuilt

@rpm you got any suggestions on any rebuilders you've dealt with??
 
ShaunCorbs said:
do you know the loop length? eg the circuit length

and anything can be rebuilt

@rpm you got any suggestions on any rebuilders you've dealt with??
Click to expand...

Circuit length is less than 10m. From this pump the iron pipe goes 2m to the left, reduces to 22mm, through the cylinder, back up to 2 inch, through a 3 port and back to the return . The pump, boiler, cylinder, and all the pipework concerned are in the same room about 3m square.
 
yea standard circulator 3 port is there as a bypass and to let the boilers heat up first before it goes into the coil need to know the spec of the pump but easy enough to get a pump
 
Philip Saunders said:
It isn't a secondary pump. Pic in the original post - it's a standard circulator but it's ancient and huge. Probably 10 times bigger than it needs to be.
Click to expand...

yea edited my post dhw bit got me
 
there should be a data badge somewhere telling you the specs
 
ShaunCorbs said:
there should be a data badge somewhere telling you the specs
Click to expand...

No badge on the dead pump but picture shows the data plate pin the working backup pump. This is WAY over the top. All the domestic circulators I've installed have much longer circuit lengths on smaller pipe and they're tiny. But they're single phase and won't fit the pipe.
On the other hand they probably won't last 40 years.

IMG_20190324_192342.jpg
 
spot on

what size flanges do you have should be marked on them dn 60 etc?

tbh easier to get the manufactures out eg grundfos, dab , wilo to give you an idea of what pump on there list you need
 
Last edited:
Flanges aren't marked but I believe they're DN60 for 2.5 inch

Getting someone out isn't simple - I'm in the north Highlands getting someone out just for some advice is a big ask. There are local tradesmen, but that pump is older than most of them, they take one look and want to sell me a hive system that lets me run a bath while I'm at Tesco ....
Really I just want to avoid spending £1000 on a direct massively over specified replacement. But if that's the only option I guess I'll have to suck it up.
 
whats your other pumps / your heating ones (pic)
 
Pump size would depend on required flow rate for recovery. Rough guess if you look at 30 mins recovery for 210 litres is about 20kW input which on an old system (82/71C) is about 0.4 litre/s primary flow and probably about 10kPa pressure drop. If the system can be run at 80/60C then the flow is about 0.24 l/s. In other words a normal domestic single phase heating pump will do the job and not break the bank.
 
ShaunCorbs said:
whats your other pumps / your heating ones (pic)
Click to expand...

Pics attached - these have a harder life that the DHW pump - 42 rads some of which are 4m (yes I do mean 17 feet) long, but they're set to speed 1 and work fine. Only one is active at a time.

Sparkgap said:
Pump size would depend on required flow rate for recovery. Rough guess if you look at 30 mins recovery for 210 litres is about 20kW input which on an old system (82/71C) is about 0.4 litre/s primary flow and probably about 10kPa pressure drop. If the system can be run at 80/60C then the flow is about 0.24 l/s. In other words a normal domestic single phase heating pump will do the job and not break the bank.
Click to expand...

I like your numbers - l looked up how to calculate this stuff and came pretty close. Give the price of a domestic pump I may well just bite the bullet and sort out the cabling to single phase. Problem will be plumbing - got to get down from 2" iron to whatever the pump is on both sides of the pump, plus the pump width, in about 450mm (after I remove the flanges and reducers).

Thanks all.
IMG_20190326_154953.jpg
IMG_20190326_154934.jpg
 
It may be a false economy to fit a domestic pump. If the one you have appears to have lasted 20 years by the state of it do you want to fit something that may last a lot less. Most domestic pumps only seem to have about 1 or 2 years warranty.
 
That's no domestic system!
No domestic pump will be warranted in that situation.
Can anyone refurb one of the pumps? Ask @rpm If not, fit what is in and keep warm and sleep nights.
 
To be honest the Grundfos commercial stuff is £5-600. I can’t see removing the pump, sending away for overhaul and refitting being that much cheaper and fundamentally it will still be a 20 year old bit of kit. Just look for a pump from reputable maker with the same length between flange faces.
 

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