Danfoss CH Pump & Inhibitor

[Davey]

Over a period of about three months, my existing, age unknown, Danfoss CH pump has gone from making a faint "do you hear that?" at night noise, to a "I can hear the pump running again" any-time-of-the-day noise. I intend to buy a replacement ready for the inevitable, it is a standard unit, but is it likely to keep soldiering on until it just expires slowly, and loudly, or is it likely to die a sudden death? In other words, should I replace it a.s.a.p., or wait until the cold spell has passed?

Secondly, the piping is all copper, the radiators, I assume, iron. Should I put some kind of inhibitor into the tank when I refill the system after the pump replacement? Assuming 'yes', which is the best brand?

TIA,

[Dave Liquorice]

Have you bled it? Loosen the large coin turn screw, let any air out and a bit of water. I might be very hot(!) and be that nasty stains anything and everything it gets in contact with black.

The wise also buy the pump isolator/connection valves as well and "rubber" rather than fibre washers to fit between the pump flange and valve. You might be lucky and be able to get the pump seperated from the valves but I wouldn't bank on it unless you know that "rubber" washers and a light smear of grease was used when the pump was installed.

If it ain't broke, don't fix it. Think of the trouble you will be in if you try and "fix" it and run into problems when the weather is cold. But by all means have the bits ready just in case it does fail.

You shouldn't need to drain down to get the pump out. Close the valves each side (hope they seal!), release the flange nuts (if you can), slide out old pump, clean of the seats on the valves, slide in new pump with "rubber" washers with a light smear of plumbing silicone grease, gently nip up the flange nuts, job done, nesimples. B-) Should only lose a pint or so of water.

[Davey]

Will definitely try that first. There is plenty of the system higher than the pump and boiler, and all rads get hot all over, but there is no harm in trying bleeding.

It is, of course, hard to get at. I have no idea who/what/how/when it was installed.

Makes good sense. It sounds as though these can go on for a long time even when noisy?

I took a photo yesterday, and it looks as though the valves above and below the pump are screwed to the pump, and the valves have the nuts, which means that removing the pump means removing the valves as well. The valves look more like setting valves to me, who is more familiar with large industrial systems than domestic ones. A pity this is not a binary newsgroup.

[Dave Liquorice]

Not normally used to control the flow rate in a domestic setting, the pumps are normally three speed via an electrical switch on the cable connection unit.

Unless you have something unusual there is a large (approx 2"), thin nut on the pump side of the valve actuator. The edge of the flange on the pump has a matching thread. These have a habit of joining themselves together never to come apart again. The pump flanges are a standard(*) distance apart and have a washer on them to seal against the valve. Once you undo both of these thin nuts and get them out of the way the pump simply(ha!) slides out.

and post the image URL.

[Roger Mills]

No. The bare pump looks like this:

with a threaded flange top and bottom. The isolator valves - which look like: or the ball-valve equivalent - have large nuts which screw onto the pump. So you turn off the valves to keep the water in the system, undo the big nuts and slide out the pump, with virtually no water spillage.

That's the theory, but it doesn't always work like that! The valves don't always actually turn off - particularly if they're gate valves - and shifting the big nuts after they've been done up for a few years can present a bit of a challenge. Otherwise, a piece of cake!

[Davey]

Ah, so the big nuts rotate around the valve body? That is not clear from my photo, they look solid with the valve, but makes much more sense. OK. so far. Now to source the recommended washers, presumably from a local builders' merchant, and I should be good to go when required.

Thanks for all the help.

[Davey]

Holy crap! Did you read the Terms etc?

[Dave Liquorice]

I see nothing that isn't on every other responsible, free, public, hosting site. What, specifically, are you objecting to?

[Davey]

Firstly, the huge size of the Terms. And for a 'free' site, this is interesting: "3. Fees. You acknowledge that TinyPic reserves the right to charge for any portion of the TinyPic Services and to change its fees (if any) from time to time in its discretion."

[Davey]

Did this last night, not much black stuff, before it ran clear, which is encouraging. But if it made any difference to the noise, it was not very significant, it's still there.

Nothing ventured, nothing gained. Next time I'm in town, I think I might buy some inhibitor, and try that.