Central heating system conundrum

[Another John]

Hoping for some guidance..

History:

- About four weeks ago I noticed the the radiators were taking longer and longer to warm up.

- I decided (for no reason other than it's never been done for 7 years) that the system is probably gunged up, and needs draining and refilling.

- Most of our radiators are at least 30 years old; it is a microbore system (dammit); inhibitor was put in when the system was last filled, 7 years ago.

- I was delayed in booking a plumber by a holiday, and by a family visit.

- While the family were here (last weekend) the system packed up altogether: no heat to the radiators, and the hot water not working well either. Then the boiler started to stall, with a "Circulation Fault" (this is a Glow Worm Flexicom HX, Fault code 25).

Current status:

- (Assisted by a Google search on the relevant fault code), I was encouraged in my belief that the system is bunged up and needs flushing. However ...

- ... two different plumbers whom I've contacted (both unavailable for weeks btw) both said there's no reason why it should be bunged up if there is inhibitor in the system.

- So could it be the pump that needs renewing? Or perhaps the 3-way valve? Or maybe there's a boiler fault? But ...

(a) the pump makes a noise like it's working (it's on speed 2 of 3); (b) and the 3-way *seems* to work, in that the relevant pipes get warm at the relevant heating stages; (c) and the boiler doesn't *seem* to be complaining, other than stopping with the Fault Code when it's had enough of trying to reach, and sustain, operating temperature.

The two plumbers I've contacted aren't available for a fortnight, and moreover seem reluctant to take on this sort of job. I am willing (and moderately able) to do "something" myself, but I'm extremely chary of doing anything, unless I know what the "something" ought to be. For example I would drain the system and refill, if I could be confident of doing it correctly -- there's ample opportunity for screwing things up worse than they are already.

If anyone's got any broad-stroke advice for my next move, I'd be very grateful. I'm well aware, btw, of the excellent section in the Wiki,

but (as I have been saying ad nauseam) I'm not sure where to start.

John "Thank goodness it's Spring"

[Andrew Gabriel]

The pump usually has a large bleeding screw on the rear of the shaft. Unscrew this and see if the rotor is spinning. Water will leak out whilst the screw is removed, so catch it and don't let it get into any wiring. It might also be black and stain furnishings. (If it continues running out black after the initial few cc's, that would imply the inhibitor isn't working anymore.)

If that's working, check for flow by feeling the hot water move along the pipe when firing up the boiler with a cold system. If that's slow (not the heating of the water, but the movement along the pipes), then either the flow is blocked, or the pump isn't pumping. Does turning the pump on to 3 make any difference? One possible failure with the pump is the impeller having disintegrated, so it has little left in terms of vanes to force the water through. This happens gradually if the pump is pumping against quite high dynamic pressure, and/or the static pressure is low at that point (causing cavitation). You would need to remove the pump and inspect the impeller to confirm this.

[Roger Mills]

My instinct says that the pump is duff. Presumably the HW circuit

*isn't* microbore, and uses 22mm pipes? If that is the case but there's still no circulation in the HW circuit, that is very unlikely to be due to gunge. First, check that the shaft is rotating, as Andrew says. If it *isn't*, you then know where the problem lies. If it *is* rotating, it could still have a failed impeller - which you can only check by removing the pump. With a bit of luck there will be an isolation valve either side of the pump, allowing it to be removed without draining down. With even more luck, the valves will actually *work*, and not be seized up!

[Dave Liquorice]

Hum, maybe had it had inhibitor in it for the first 23 years?

I've never managed to peer into the hole and see the end of the shaft. It has a slot in the end though so a flat bladed screw driver can be used to see if it turns freely with the power off or is rotating with the power on (careful...).

Dribbles out on my gravity systems old towel does the catching.

Or that it didn't have inhibtor for the first 23 years... The water in our system is clearish black because it's a mix of old/new systems that is now inhibited.

If going to all the agro of removing the pump you may as well just replace it. How old is it? 30 years if very good going 7 well it might be knackered if it's working hard with a microbore system.

If they are gate valves I'd put money on them a) being siezed b) if not siezed unable to shut off c) be siezed to the flanges of the pump.

Be prepared to replace the valves, choose the ball type not gate, use a lighly greased (silicone not mineral) "rubber" washer not a fibre washer in the flange joint.

With luck (ha, this a CH pump) you might be able to get the old valves off the pipe work and fit the new ones onto the stubbs (possibly reusing the olive and nut) and the spacing will still be correct for the pump to slide into. Don't tighten the valves onto the pipes until you have fitted the pump onto the valves and also checked that the olives seat well into the new valves. One or both olives may have to be removed (cut off).

[Another John]

Thank you very much Andrew and Roger -- Roger develops Andrew's advice and says this:

Yes.

Lights are going on (though they may go out again soon!): I have used the immersion heater for the last couple of days to heat the water. It heats it to much hotter than the gas CH system .... and therefore it has been puzzling me why, at "hot water ON time", the CH starts to try and heat the hot water. I can hear the pump (and boiler) going for ages before I override and turn it off, muttering "WHY are you trying to heat water which is already bloody hot??"

If your (joint) theory is correct, that the pump is nadgered, then this would explain that[1]: no impeller worth speaking of, but everything else working, and so the system is trying to use a pump that isn't pumping.

So I need to replace the pump, as a possible fix. It's a Grundfos Super Selectric. It was > First, check that the shaft is rotating, as Andrew says. If it

Yes! there look to be isolation valves there!

No idea on the life of a pump: this one is 7 years old (almost exactly), and (of course) is used on demand, 24/7/365. Is seven years a reasonable life expectancy for a CH pump?

John

p.s. The system was renovated by one of the best respected (and expensive) firms in the area, but they are singularly uninterested in fixing as opposed to installing systems (I can see why, to be fair).

[1] Hmm - or would it. What is the hot water thermostat for!?

[Another John]

...

Dave -- thanks very much for your response, which adds to what I've got already from Andrew and Roger.

John

[Andrew Gabriel]

IIRC, the motor axis should be horizontal, or slightly angled down at the bleed screw end. This is to ensure the bearing which is lubricated by the water can't get air trapped in it, and lose its lubrication.

[Roger Mills]

If the water in the cylinder is above the cylinder stat set temperature, the boiler shouldn't be trying to heat it at all - just as, when heating the HW with the boiler, the boiler should shut down when the target temperature is reached.

Which makes me wonder what the setting is on the cylinder stat. If the water hasn't been getting hot because of (say) a failed pump, might you have turned the stat up in the hope of making the water hotter? It seems possible that when using the boiler, the water never got hot enough to satisfy the stat, and the boiler may have run for the entire timer on period. What happens now if you turn the stat down when the boiler is running? Does it stop?

That's a good start - but whether they work is another matter!

Pumps should hopefully last longer than that - but may not. I can only remember replacing mine 3 times in 38 years - and in two of those cases the pump hadn't failed but was changed for other reasons.

[Another John]

Hmmmmmmmm !!! Must check on that then. Like I said before, the installers were (still are) one of the best respected firms in our area. Hmmmmm

[Another John]

Andrew's post has just given a big fat clue: following up on it, I have found the documentation from the installation in 2008: the leaflet for the Grundfos pump explicitly says what Andrew said: they should not be fitted in the vertical plane - there are diagrams, and the explanation why it shouldn't be done! :-(

I remember moaning about the previous installation to the new plumber, that the pump was fitted in a confined space under the floorboards in the bathroom. The new plumber put it in the airing cupboard, which I was very pleased about: great access. It never occurred to me that they would fit it incorrectly! (Beautiful neat job, venting spurs, isolation valves, bypass valve, and stuff ..... but the pump not fitted as per specification!

Looks like I need to take it off, and look at it. Or rather, get a plumber to fit a new one in the right orientation.

John

[Chris French]

Or it might be that the water heated by the immersion heater doesn't go down the tank as far as the tank stat (at least not heated up to 60C or whatever)?

Our immersion doesn't heat as much water as the boiler supplied pipe coil and I suspect, though haven't confirmed that when the immersion switches off, the tank stat would still be calling for heat

[Dave Liquorice]

Or vertical, bleed scree up.

My IIRC says up at the bleed end...

Can't find a copy of the installation instructions online or in the dead tree system. B-(

[Andrew Gabriel]

Your symptoms are not obviously due to pump bearing failure though. That causes the pump to get noisy and vibrate. I suppose it could seize eventually, but I haven't come across that.

Can't you just swivel it around on the pipe by slackening off and then retighening the isolating valves?

I don't think this will solve your problem though.

[DerbyBorn]

Another John wrote in news:lalaw44-787A90.19025122042015@[216.196.109.145.hva.nl]:

A good plumber can bend and connect pipes. They are useless at reading instructions.

[Another John]

Ah well I've never mentioned that for some several months (a year even?) we have had a vibration noise in the system (not harsh or noisy, but present and annoying). I have always put that down to pipework somewhere fractionally shifting, into contact with joists/boards/whatever. I had been going to mention this to the plumber who would be coming to fix my current problem. I now see that it could (possibly) have been the pump. Or possibly not. Possibly a separate problem entirely.

This (all) illustrates the infinite variety of CH difficulties!

Um - not sure what I'd be trying to achieve there? (Sorry to be thick Andrew -- trying my best to keep up here :-)

John

[Roger Mills]

Is the pump installed in a vertical or horizontal pipe, and in what way do you believe it to have been installed wrongly?

[Better still can you upload a photograph of the pump installation somewhere, and post a link to it here?]

AIUI, the axis of the pump motor needs to be horizontal or sloping up slightly towards the vent end, but *never* down.

I think Andrew is assuming that the pump is installed in a horizontal pipe. If so, the motor axis can be made horizontal simply by rotating the pump body about the pipe axis. You can do this by slightly slackening the compression nuts on the remote ends of the isolating valves, rotating the pump (and valves)[1], and then re-tightening the nuts. They only need slackening a bit - not enough to cause water leaks

- but put an old towel underneath, just in case!

[1] Or, you could slacken the large nuts which fasten the isolation valves to the pump - and just rotate the pump and not the valves - but they are more difficult to undo and re-seal. You'll have to undo them, of course to remove the pump, but you can then clean up the faces and use new rubber washers - which you can't do if you're just slackening them for rotation.

[Johnny B Good]

Your memory serves you well. The leaflet does indeed mention slightly angled up. Angled down, even very slightly, is a big no no.

[Johnny B Good]

I'm not sure whether you're referring to the pump being fitted into a vertical pipe run or having the pump body orientated with its shaft in a vertical plane.

Since it's not clear as to exactly which of those two possibilities you mean, I feel impelled to clarify the reference to avoiding at all costs positioning the pump shaft in a vertical plane (only possible when fitted into a horizontal pipe run).

Fitting the pump into a vertical pipe run is the recommended fitting option, preferably pumping upwards. However, downwards flow is allowed but only if an effective air purger and air vent is fitted before the intake side of the pump. If the vertical pipe run isn't absolutely vertical, you have to rotate the pump body so that the motor end of the shaft is level or slightly raised.

If you fit the pump into a horizontal run (eg under floorboards), orientation is somewhat more critical in that you are limited to positioning the pump body so that the pump shaft is horizontal with no downward tilt or no more than just a slight upward tilt. Also, never orientate the pump body so that the pump shaft is pointed vertically (ie pump body up).

This is the bit of 'context' that confused me as to exactly what you meant. Our pump has always been fitted into the vertical pipework

*in_the_airing_cupboard* for the past 3 decades. Admittedly, the original pump only lasted a mere 7 to 10 years before I tried a succession of alternative 'freebies' provide by my father before finally (and reluctantly) giving in and buying a Grundfoss pump some 13 to 17 years ago (the receipt has mysteriously vanished so 'best guess').

The difference between this Grundfoss and the one originally fitted was like night and day. The original had always produced a low level of vibration into the pipework from day 1. Provided the pipework wasn't contacting any other hard parts the resulting quiet hum was just a reassuring minor distraction. The new pump, however, was *so* silent, I couldn't believe it was actually running without kneeling down by the airing cupboard to listen more closely and to check the flow and return pipework to confirm that the temperature rise was on a par with previous experience.

It is possible to perceive a quiet hum in the pipework just at the threshold of hearing in our bedroom when all is quiet in the late evening. The pump has remained just as quiet and effective ever since it was installed all those years ago which bodes very well for the condition of a CH & HW system that's served us well these past three decades. I never bothered with a maintenance contract of any sort and I doubt the outlay on running repairs and maintenance has averaged more than 30 quid a year tops so it owes us nothing.

[Another John]

OK ok ok calm down John! [i.e. me!] I feel such a dumbo at times: all this talk of vertical mounting, vertical axes, etc etc confused me (I did languages and literature fellas ...)

The pump is mounted in a vertical pipe. This means (**of course**, I see now) that the pump *shaft* is horizontal. And in fact the Grundfos leaflet, when I read it rather than look at the pictures, says "It is preferable to mount Grundfos circulators in a vertical pipe, pumping upwards." This is exactly what I have got: pictures!

So: the reputation of my local firm ("highest reputation in the area") is restored, and I recant my implications of earlier :-)

And: I'm now wondering what my problem is. I've now turned the CH off completely, rather than have the system doing whatever it's been doing, and having the boiler go into Fault Mode every now and then.

I hope you chaps appreciate how candid I've been! I'm embarrassed about mis-interpreting the recent suggestions from Andrew and Roger and reaching a false conclusion!

Off to do a day's gardening for an old lady now: a task I feel more at home with :-D

John

[DerbyBorn]

I have elevated your Plumber to being a Heating Engineer!