Help - need to replace circulation pump!

[jezboxley]

Hi,

I had a bit of a nasty suprise this morning - our trusty old Grundfos series 3000 central heating circulation pump burnt out, started oozing a black gunk from the casing and stank the entire house out. The pump was at least 30 years old so it had a good innings and i'm confident to say that I now need a replacement pump, but the problem is that I do not know what to buy to replace it.

To give you and idea of the current setup the pump was quite large and had a port to port size of 180mm, my house is on 4 floors and the heating is supplied through a combination of 22mm copper pipe connecting to 15mm copper pipe and also to some manifolds which have some rather old black plastic microbore piping roughly 10mm in diameter running off them to feed the radiators. All radiators are fitted with TRVs. The header tank for the central heating is situated roughly 10m above the pump.

According to the Grundfos website a suitable replacement for a series 3000 is one of their new ALPHA Pro 15-50 130 pumps, but according to their literature this has a maximum head of 50dm (I assume this to be 5m??) and a port to port size of 130mm. So to me the first problem is that my head of 10m to the header tank will be too much for this pump and the port size of 130mm will be too small for the gap my pump will leave. Am I correct over these?

In light of these potential problems I looked at one of their other pumps, the MAGNA 25-100, which has a maximum head of 100dm (Again, I assume this is 10m??) and a port to port size of 180mm. It also has 1 1/2" gland connectors so it appears it should fit in the gap a treat and work with the height of the header tank. It sounds potentially like the ideal replacement. I then looked at the price and saw that this pump was listed at over £400! I was expecting the pump to cost more than the £50-£60 quid pumps you can buy from the local DIY stores, but was a bit suprised at this cost.

Am I correct in thinking that this MAGNA 25-100 is a suitable replacement for my old pump considering the height of the house, small pipes etc., or will it turn out to be some industrial monster that'll be way too powerful for what I need and I would be better off going for something smaller? I'm not too worried about the cost if the pump is a good replacement for the old one - I just don't want a pump that is too weak or too powerful for the job.

Any thoughts on this would be appreciated!

Thanks,

Jez

 

[ChrisR]

Never seen a pump head seen in dm - perhaps they'll use fathoms next?!

The house height doesn't determine what pump head you need, but the resistance of the pipework. The pipes are a loop, so the water going down pulss the water up the other side, if you see what I mean.

Olde pumps used to be 180mm, and there are spacers commonly available to make up the difference - any plumbers merchant.

Grundfos like to specify their more expensive pumps (Alphas). If you go into a different part of the site you see a normal 15 - 50 as the replacement. They do point out that over the lifetime of the pump, you save money on electricity if you use an Alpha, though.

I would put a 15-60 in, which provides a small but significant extra head (6m instead of 5m), because realistically, old system have sludgy resistances, especially microbore. You can always turn the thing down, it has 3 speeds.

 

[jezboxley]

Chris - thanks for your reply. Looks like you've saved me a good bit of money. I owe you a beer!

I've now got myself a 15-60 as you suggested and just waiting on the spacers.

Thanks again,

Jez

 

[Agile]

If you have completely drained the system you could add a few extra mm of copper pipe.

Its normal to run CH pumps on the middle setting (2).

Its always a good idea to replace pump valves when an old pump is being replaced but you must use the gate type.

If the water is anything other then clear you should add X400 or similar to clean it out otherwise you new pump may fail rather sooner than later!

Tony