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
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
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
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
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.
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
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.
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
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.
Firstly, the huge size of the Terms. And for a 'free' site, this is
"3. Fees. You acknowledge that TinyPic reserves the right to charge
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from time to time in its discretion."
No. The bare pump looks like this:
with a threaded flange top and bottom. The isolator valves - which
look like: http://www.screwfix.com/p/gate-pump-valve-22mm/81629 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! <g>
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
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.
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.
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