Central heating pump – help!

Some ten years ago maybe, my central heating pump died. It’s an ancient one-pipe system and the pump looked like something out of a nuclear submarine (seriously, it was a foot across and had alternate wiring connections for 3-phase). I replaced it at the time with a “Wilo Gold 50″ pump (and about 6” of copper pipe). This has now died (probably full of shite I’m guessing).

Looking at replacements and the choice is bewildering. In particular, they all seem to have clever variable settings which mean nothing to me. Take this:

http://www.anchorpumps.com/media/downloads/2401/CP%2050-60%20Operating%20Manual.pdf

Control modes
Variable differential pressure (?p-v):
The differential-pressure setpoint H is increased linearly
over the permitted volume flow range between ½H and H
(Fig. 2a). The differential pressure generated by the pump
is adjusted to the corresponding differential-pressure setpoint.

3 speed stages:
The pump runs uncontrolled in three prescribed fixed speed
stages. (Fig. 2b).

What does that even mean? How should I be setting it to, well, just pump? I don’t want to set it too high and flood the house, nor too low as it doesn’t actually do anything. I’ve no idea what a H is or why I might want half of one.

Are these things serviceable? Is it worth me trying to take it to bits or should I just skip it and replace? If so, what with? I was looking at this: http://www.screwfix.com/p/grundfos-ups2-15-50-60-central-heating-pump/42635 – as I believe Grundfos are well regarded, and it’s supposed to be a direct replacement for the Wilo, though whether it’s a direct replacement for my Submarine Surplus who knows.

Cheers.

Firstly, i assume you’ve popped off the rotor end cover/bleed port and span the rotor with an allenkey/screwdriver to make sure it isn’t jammed?

These pumps have very little starting torque, and often are fine once they’ve been round a couple of times!

PS, it’s the stainless steel cap on the end of the pump with the large screwdriver slot in it!

(take an old towel / and or ice cream tub with you when you remove it, as a bit of water will dribble out when you remove that end cap)

I haven’t – it’s kinda hard to get at so I was going to take it out. I’ll have a go though, ta.

On the upside, I had the foresight to fit isolation valves either side when I fitted it, so don’t have to drain the entire bloody system. Small victories.

As above, try to get it moving manually first

If it is knackered (check if it’s blown a fuse from being jammed too) then i wouldn’t worry too much about all that variable speed pump nonsense. Since a heating circuit is closed loop (boiler heats water, pumped to Radiator, where water is cooled, and returned to boiler) it’ll pretty much work with any flow rate as all that happens is the mean water temperature will change to rebalance the total heat flux (Qdot = Cp.Mdot.deltaT).

I’d buy a basic pump, if it’s got 3 speed settings, set it to 1, and try it. If for some (unlikely) reason you don’t get enough heat out of the radiators then you can always turn it up.

(generally, because deltaP varies with the square of Mdot, extra pump speed really doesn’t get you much, but for radiators with very restrictive feed pipework then a higher pump speed can be required, but that obviously comes with a higher electricity consumption penalty)

Cougar
On the upside, I had the foresight to fit isolation valves either side when I fitted it, so don’t have to drain the entire bloody system. Small victories.

Unless those valves are seized solid after 10 years of not being turned…… 😆

Ours is a circulating pumps cp53 (I’m not anal it just happened to be right there when I put something away under the stairs)

Three speeds, pretty basic apart from that

I’d buy a basic pump, if it’s got 3 speed settings, set it to 1, and try it. If for some (unlikely) reason you don’t get enough heat out of the radiators then you can always turn it up.

Looking at the Wilo, it’s got 3 speeds and set on ‘3’ currently. It’ll probably need the grunt I think – the entire system is woeful, probably more sludge than water. The long-term plan is to fix it with a new house.

it’ll pretty much work with any flow rate as all that happens is the mean water temperature will change to rebalance the total heat flux (Qdot = Cp.Mdot.deltaT).

I now know how users feel when I try to tell them what’s wrong with their computer.

Firstly, i assume you’ve popped off the rotor end cover/bleed port and span the rotor with an allenkey/screwdriver to make sure it isn’t jammed?

The hole is smaller than I expected, maybe 6mm across. I can’t see any blades, it’s just not big enough. I’ll have a poke about with a small Allen key.

No dice. There’s nothing to be had there beyond the spindle I don’t think, unless I’m being inept.

Unless those valves are seized solid after 10 years of not being turned……

Valves are fine. The screw connectors on the end, however… Anyone have some 1.5″ spanners? Argh.

Hang on.

The pumps are supposed to be ‘1.5″ BSP’ connectors, and Screwfix lists a 2″ pump spanner “for use on most nuts next to domestic circulating pumps.” Is that the same thing?

No you won’t see the rotor, just the small end of the shaft, which should have either a screwdriver slot or an allen key rebate in the end, allowing you to turn it with one of those tools!

1.5 BSP is the thread size, 2″ is the across the flats dimension of the nut iirc

which should have either a screwdriver slot or an allen key rebate in the end

Ah! Gotcha.

Or you partially pull off the plastic cover until it engages then turn it with that, depends on model

Pump seems to spin freely. Well, there’s a bit of resistance, but not a huge amount. Hm.

I suspect you have an open vented heating system so pump speed will need to ensure that it doesn’t pump over the open vent as that will cause corrosion.
One pipe systems usually have low resistance so pump could be set very slow.

Pump spins, there’s power to it I think (a tester says 12V, but it’s a cheap shit tester so I believe it’s lying; surely with mains there’s either power or there’s not?), the capacitor looks in good shape so… it’s time for a new pump and a big spanner isn’t it.

I suspect you have an open vented heating system

How would I know? I believe it’s all fed from an (open) water tank above the cistern, if that’s what you mean?

/sigh

Pump acquired, non-useless mains tester acquired, the spanner is next-day only in Screwfix and all the other plumber’s merchants I know of are shut (presumably because plumbers don’t work weekends).

Extra duvet on the bed tonight then. Cheers all.

It’s a 10 minute job to swap them out, assuming the gate valves haven’t seized in the open position (you did turn them from time to time, right?).

The variable pressure / flow settings are there because pumps need to meet energy efficiency requirements, since there’s no point running it flat out when all the TRVs are closed, for example.

I’d try it on the proportional pressure modes first and then switch back to constant speed mode if you think heating performance has dropped. Don’t use proportional pressure modes if you have an automatic bypass valve for obvious reasons.

For future readers, this was handy:

http://www.plumbteamltd.co.uk/heatingpump.html

At your own risk applies.

When we had a central heating fault I disconnect the pump and put a plug on it to fully test. Kept out radiators warm and I found the electrical fault elsewhere in the system, turned out it was a pipe mounted thermostat

As an aside, fit a magnetic filter at the same time, will help keep the system clean.

When we had a central heating fault I disconnect the pump and put a plug on it to fully test

Yeah, I’d already considered that briefly. Figured though, if the mains tester goes ‘bing’ that’s close enough.

As an aside, fit a magnetic filter at the same time, will help keep the system clean.

http://www.telegraph.co.uk/lifestyle/interiors/renovating/9618280/Are-magnetic-filters-for-central-heating-a-good-idea.html

❓

I was wondering about this, whether it’s worth some sort of treatment or other. But like I said, it’s an ancient system with an old back boiler, so I don’t really know how to go about it or if it’d help. I suppose really I could do to take all the rads off and flush them (I’m pretty sure they’re crapped up, they have cold spots), but that’s going to be challenging with no bloody water supply! Most Internet advice seems to assume a modern combi system.

… I’ve also no idea where I’d site such a thing.

On the upside, I had the foresight to fit isolation valves either side when I fitted it

Presumably in that case you’ve already got the tools you need to fit the pump…

It might be worth draining the system down when you replace the pump and bunging some Fernox F3 or similar in for a week or so. Drain again when fully hot and refill with some inhibitor. F3’s pretty good at shifting muck, though probably not up to the job if your system’s really sludgy.

Presumably in that case you’ve already got the tools you need to fit the pump…

lol

My house, being built cheaply in the late 1980’s has that horrible small bore pipework. To clear it, i had to drain the system, and force mains pressure cold water backwards up through the system drain point, turning on one rad at a time. The dirt, rust and rubbish that eventually spurted out the vent tube was incredible! (i had attacked a bit of hose pipe to the vent tube above the loft header tank, and run it down into the bath to allow the gunk to be washed out!

Got the fecker. Cougar 1, pump 0.

Now for the new one. I may be overqualified, according to the instructions “this appliance can be used by children aged from 8 years and above…”

And, we have heating.

As far as I can tell, the variable differentiation thing is for rads with TVRs. The fixed speeds go from 1-3, so I’ve arbitrarily stuck it on 2. So far, I’ve not died.

Now to put the house back together. I’d to take the bloody door off </Michael Caine> to get the carpet up!

Vital statistics:

Doors removed: 1.
Pictures unhung: 1.
Pieces of furniture moved: 1.
Floorboards lifted: 3.
New tools bought: 2.
Pounds spent at Screwfix: 128.
Screwdriver bits used: 6 (plus a 10p coin for the bleed screw).
Mouse carcasses found: 1.
Swearwords uttered: Many.

Thanks again to all who offered advice.