Not the most exciting topic, granted….

But, our central heating circ pump has been on the way out for some time, and has now all but given up the ghost & needs replacing. It's a Grundfos 15/50 Selectric.
I think our system is an open one, but can't tell you much more than that.

All the literature for the pump recommends that the pump should be plumbed in to pump upwards as this stops air getting trapped in the pump housing & knackering the pump, unless you have an air vent fittted above the pump. I am not sure what a vent looks like, but am pretty sure we don't have one. The pipe above the pump disappears off into the loft, and there's a pipe running parallel this this one (same dia.) with a short branch between the two about a foot above the pump.

I am guessing that the lack of air vent/pump facing downwards is why our system is quite noisy & we often have to bleed the radiators. Does anyone know if this is the case?
Why would our system be plumbed in to pump downwards when the pumps seem to all recommend operating upwards, and why do we appear to have no vent?

Anyone know how easy it is to fit a vent to the system? And how much it's likely to cost?
I spoke to the other half's Dad last night as he's a retired plumber. He reckoned it was fine to just run the pump downwards and from looking on the internet last night there are plenty of others who advocate this, but I don't see how this is a sensible thing to do when the pump manufacturer recommends you don't do it and the symptoms we are experiencing with our system seem to tie up with the fact that our pump is pumping down, not up.

Any help appreciated!

I take it that's a no, then….

(shameless attempt at a bounce)………

Pump upwards usually is in reference to the pump body, basically, where the grundfos label is, there is a silver bleed screw, this needs to be facing upwards or outwards to stop air trapping, if you had that facing downwards, the pump would trap air, any other orientation is fine

the pipe that goes to the loft is most likely the open vent / cold feed arrangement, so should be ok. Saying that not many plumbers can get them in the correct orientation. If it is a close coupled arrangement the two tees should be no more than 150mm apart, and they should be taken off a horizontal section of pipework. If you can take a photo mail it to me and I'll have a quick look.

paulosoxo – yeah, the pump is fixed on a vertical pipe with the pump shaft horizontal – the grundfos logo on the pump is actually upside down & the arrow on the pump also points downwards, making me assume that the pump is pumping in a downwards direction.
It's this, that Grundfos don't recommend as air gets trapped in the pump housing apparently and knackers the pump/causes the system to be noisier.

Bear – I did wonder if the parallel pipe was some kind of vent. I have just taken some pics but there is no mail address in your profile.

We plan on fitting the pump this weekend. The current one is really noisy & only works intermittently.

it's fine like that

stumpy, sorry thought there was :

timATj-twren.eclipse.co.uk

Cheers Bear….pics sent

paulosoxo – I hope you're right!

EDIT – why don't I just post them here (D'OH!!)

copied from e-mail:

Pics attached. I took one of the pump with the pipes going up from it and one below.

As you can see from pic595, there's 2 22mm pipes going upwards (one coming from the pump) with a connecting piece between them. Both pipes disappear into the loft & as of yet I haven't investigated what's up there, but have to chuck some boxes up there later anyway so will probably have a poke around.
In the second pic, the pipe that comes out of the pump goes into a T and from there into the 2 motorised valves. Before it gets to these valves, there's another pipe coming off it that goes to a large red stop tap.

I think the scale is from a previous leak – can't honestly remember!

Do you think that the 2nd pipe is the required vent pipe? Sorry about the lack of indepth insight!! I can obviously provide more info if required.

he's definitely right its not pump direction thats causing you problems

configuration of feed and vent pipes above pump would be worth checking as would a dry tank

the pipe that continues vertically up from the pump should connect to the bottom of your header tank

the other pipe running vertically parallel to it should bend over the top of the tank to vent the system

edit -all that scale and crap not a good sign 😕

Excellent – I will check that out later.

Thanks for everyone's help!

Your main concern is that those pump valves WILL leak from the screwdriver slots when you try and turn them off.

I'd bung that

by the way. you cang remove the 4 allan bolts from the pump, and change the heads over if needed. I usually take the pressure out of a pump that way (slackening the bolts rather than removing them)

i'd strip it all out and rebuild the lot 😀

some other ideas
whats the vertical height from pump to tank ?
what vertical height does the vent pipe extend above the tank before it bends back down?
how skanky is the water in the tank?
worth checking carefully for leaks

reason i ask is that doesnt look like a very old pump and in a well installed system grundfos usually last forever so some other factor is knackering your pump and probably will again- edit

UPDATE:

Massive DIY fail. The fastener came off the top valve but no way it was budging off the bottom. There's loads of mineral build up or something siezing it solid.
Also, even with the valve 'shut', there was a lot of water coming from the top valve, with the nut opened about half a turn. I expected a small mount and then nothing from the top one.

Looks like I'll be getting someone in to sort it!

Some more info:

– vertical height of pump to tank – must be at least 1.7m. It's 1.3 to ceiling, then the thickness of the ceiling/insulation and the tank is sited on a board on top of the joists.
– The vent just about clears the header tank. It doesn't really come back down – it comes up, runs horizontal and there's a very slight downward kink into the tank. Tank must be 50-60cm tall.
– water in the tank is pretty clean/clear – you can see the fittings a the bottom of the tank.

Does seem that something isn't quite right though…….

oh, just mailed you back and can see you've loads more advice!

I've a clever freeze kit thing if you need to use it to change the valves and are anywhere in the se corner of kent.

There are a couple of isuues with the open vent / cold feed combination, but as that pump has lasted a long time they are not causing too much of an issue. The leak will though because it will introduce fresh water into the system, which contains oxygen which in turn leads to corrosion and sludge build up. And as Paul says they WILL leak without fail!

if it's all back together now, and not leaking, buy some bungs,

http://www.bhl.co.uk/product/REGIN_REGR05_RADIATOR_VALVE_CHANGE_KIT
bung the header tank, slacken the 4 screws, crack the pump seal from the body, catch the water, split new pump (providing it's a grundfos too) pull old head out, make sure rubber gasket is still in body, and put on the new head and do up the bolts.

The bungs airlock the system, you'll probably get 1/2 a bucket of water out. Don't try and bung an elson/combined or primatic, but it looks like a fully pumped S plan you have , so it should be fine

my two penneth

height to tank sounds fine and clearish water in tank is better than mud
vent should ideally rise >450mm above tank to prevent water surging over as the pump stops and starts which draws in oxygen – not saying this is the cause of your pump failure but its an easy thing to upgrade/eliminate

did the two vertical pipes check out as above?

i would say from the photos and your description that theres not a lot of water in the system above the pump
so you could consider draining it and changing pump and pump valves – tie up the ballvalve -bail out the tank with a tub and a sponge- drain from a lower point just til the pump is dry (or drain into a bucket from the pump head) and replace the lot ( gate type valves)

make sure the leccy is safely off to pump 😯

Bear, thanks for the offer of freezing kit but I think if it gets to that stage I'll be calling someone in – and I'm up nr Peterborough so a fair way away..
I need to check with my partner & her Dad, but I have a feeling that pump is not that old. I seem to remember her Dad doing something to it a while ago (he may even have replaced it). My partner already lived here when I moved in, and I think something was done with the pump before I moved in (4-5 yrs ago). So it's potentially not been in there for that long….
You mention a couple of problems with the cold feed/vent – are they the problems mentioned by bigeyedbeans?
When you say leak, do you mean the fact that the valves must be leaking due to the build up of cak around them?

Paulosoxo – I did consider getting bungs and doing it that way. It does look though like I'll have to change those valves too – not sure they are doing their job properly!
Cracking the pump sounds like it could be a go-er though but if I replace the valves, I might as well change the whole lot as well…..?

bigeyedbeans – what do you mean about 'did the vertical pipes check out as above?

what do you mean about 'did the vertical pipes check out as above

the pipe that continues vertically up from the pump should connect to the bottom of your header tank

the other pipe running vertically parallel to it should bend over the top of the tank to vent the system

Sorry – yeah, one pipe goes into the bottom of the header tank and the other one exits just above it (as described above).
It doesn't really come up & over, but just past the top of the tank, then horizontal, with a small kink down into the tank. There's a small hole cut into the corner of the lid that this can can deposit through.

Does this sound right or perhaps it could be the cause of air getting in?

One thing I did think of is that we had the radiator in one bedroom replaced a couple of yrs ago as it was corroded and leaking and had another one done about 3 months ago. COuld these leaky radiators (they were leaking around the pipe joints at the bottom) have been allowing air to be drawn in, knackering the pump?

its kind of important which one goes where- plumbers have been known to get them the wrong way round

as for the leaking radiators most likely just a symptom of a general corrosion problem not the cause of it

Put the open vent into a glass of water with the hot water on and the pump running, if it sucks the water in, then it's pulling air in there

Oooooh, good tip, I'll try that.

Apologies for the delay in getting back.
Best practice would be to take both the cold feed, and the open vent pipe of a horizontal section, making sure that they are within 150mm of each other. This allows the air to track along the top of the horizontal section and out the vent, whereas the way that you have water can be forced up the open vent. Also the open vent should be a minimum of 450mm above the WATERLINE in the expansion cistern, and should terminate inside the cistern but not in the water, remembering that the water level will rise when it is heated.
As you have replaced a couple of rads due to corrossion I would suggest that you do have an issue with fresh water as a well designed system, with the correct level of inhibitor should last a very long time. Get the leaks sorted as any leak from the cold feed pipe to the pump outlet will be drawing in air as it is on the negative side of the heating system.