CH pump expiring?

[Tim Downie]

Woke this morning to a cold house. Had a new CH boiler installed about a month ago that's been working well.

Checked the boiler and it had tripped out due to overheat. I reset the boiler and noticed that the pump wasn't running. Whacked it with a big screwdirver and it gurgled into life.

The pump is about 12 years old. Should I just replace it now or is this likely to have been a one off sort of thing? I know it's not in it's first flush of youth but it's not too hard to give it the occasional whack if that's all it's likely to need.

(BTW, the system was well flushed before and after the new boiler was fitted. I don't think there's any excess crud in the system)

Tim

[Guy King]

The message from "Tim Downie" contains these words:

Quite probably dying. It may simply be clogged up with clag, so I'd take it out first for a look-see.

[Paul Andrews]

I think the only surprising thing is that you didn't change the pump when the new boiler was fitted.

[Tim Downie]

So, aside from have a dig at possible penny pinching, do you have anything useful to say?

Admittedly it would have been easy enough to do but I've known many CH pumps to last much longer. Why change a working pump?

Tim

[Roger Mills]

It *could* be a one-off - so I wouldn't rush out immediately and buy a new pump. However, if it does it more than a couple of times, I would certainly replace the pump - no-one wants to wake up to a cold house on a regular basis! Even if it doesn't fail repeatedly, it may be a wise precaution to replace it before next winter - but at your leisure, rather than as a desperate emergency.

Was the control system also updated when the new boiler was fitted and - in particular -were TRVs fitted to most of the radiators? If so, you may wish to consider installing a Grundfos Alpha pump - which varies its output according to demand, and will turn the wick down when a lot of the TRVs are shut, reducing not only noise but also electricity consumption.

[Paul Andrews]

If the pumps been working for 12 years, it's only a matter of time before it goes. You spend £X on a new boiler, have to re-do the pipework and then pass up the chance of fitting a new pump (what do they cost? £50) at the same time . Now you have some new hassle to go and get the pump replaced, when you could have avoided it, so you haven't saved money or time, or disturbance.

I just hope that anyone else thinking of replacing an old boiler that's been around a long time will think about your experience and go that extra bit further and replace the pump too. I'm a bit suprised the fitter didn't ask as a matter of course.

Being goody two shoes, we had a new boiler and replaced the pump, thermostats and controller etc, so apart from the main pipework we've got a new system. Of course it might still break down, but it won't be down to old age.

Anyway, I guess if you are going to have a pump failure, now is a good time - it's not really cold.

Yes, it's a bit of a dig, but I wish you well with the replacement and anyone thinking to change boilers - take heed!

Paul

[Mogweed]

Our house was built in 1972 and the central heating was installed at the same time - we're still on the original pump! And, the guy who changed the boiler for us about 10 years ago said that if ever the pump did give up the ghost, try to have it repaired rather than having a crappy new one, as they "don't make 'em like they used to" :o)

Mogweed

[Harry Bloomfield]

Tim Downie used his keyboard to write :

Ours is 24 years old this year and still working any problems and absolutely quiet. Its predecessor lasted just six months and was changed under guarantee. So my suggestion would be to leave it for the time being if its not noisy or repeatedly failing to start up - what has happened might just be a one off event.

[Tim Downie]

I think I'll take it out and make sure it's de-clagged at least as per Guy's suggestion.

No because they're there already.

That's a very timely answer because I was just about to add a query about variable flow pumps and that sounds like just the business. Cheers.

Tim

[Tim Downie]

Thanks. Will do.

Tim

[Tim Downie]

Well you could say that about anything. I've been kicking round for 49 years so I suppose my days are numbered.

True is would have been easy at the time but I don't find it easy to throw away things that still work. I would like to have hung on to my old boiler longer, my glued up heat-exchanger seemed to be working fine. Besides, fitting a new pump is no guarantee of assured long life. All the bits in my CH system that have failed all did so within 6 months of installation (apart from the heat exchanger). The replacements have soldiered on for years.

Old pipework?? Sounds a bit dodgy to me! ;-)

Tim

[Tim Downie]

Just a quick follow up question (or two). Would a varible output pump like this be used in addition to an automatic bypass valve or would it make one redundant? Any idea how the pump actually senses the TRV shutdown? Pressure transducer?

Tim

[Roger Mills]

A lot depends on whether your boiler needs pump over-run to carry away the residual heat after it stops firing. If it *does*, there *must* be somewhere for the over-run flow to go - even if all the TRVs and/or zone valves are shut. So fitting a variable output pump doesn't do away with the need for a by-pass if you would otherwise need one.

My understanding of how an Alpha pump works isn't perfect - but it's something like this. A conventional pump often has 3 manually switchable speeds - each of which produces a different pressure vs flow curve (if you restrict the flow, the pressure rises).

An Alpha pump also has 3 manually selectable speeds but, in addition, it has an automatic mode. In the automatic mode, it varies the speed between the highest and lowest manual speed in an attempt to keep the output pressure constant. So if a few TRVs close, it reduces the speed to prevent the pressure from rising. ** But it can only do this within limits. When the speed gets down to the lowest setting, any further reduction in flow *does* result in a pressure rise. This is actually good - because you need this to open the auto by-pass valve when all the TRVs are shut.

I think the above is more or less right. If anyone has a better explanation, I'm sure they'll give it!

** I'm not sure how it senses pressure - there's no obvious water-side transducer in my Alpha pump. My guess it that does it via motor torque - which it probably computes as a function of speed and current.