central heating pump cavitation when hot wilo Gold R550 pump,

[M7R]

I found this site via google and it appears to be the best place to ask this question, so hopefully some one can help.

a year ago me and the wife got our first house, a nice 50s semi and as a bonus the old lady who lived there before us had had a new boiler fitted back in 2008, a Viessman VITODENS 100 ( the boiler before was a baxi back boiler as we still have the gas fire) at the time the new new boiler was put upstairs in the airing cupboard, new controls and wireless stat fitted, and all the old rads fitted with thermostats, plus a new hot water tank was fitted.

When we moved in back in dec 2010 i noticed the pump wasn't the quietest thing, but I had just moved out of my folks place which was a new build with a all singing all dancing beast installed...

I changed most of the rads last spring as the old rads were from the 60s and gave off no heat! so now I have the following fitted:

2 existing curved rads from the 60s, no fins. 1740mm x 620mm and 1270mm x 620mm (Both of these plan to be changed in the spring for 800 x 600 doubles, which is a bit over kill according to the online calculaors, however the way the bay is built does't keep in masses of heat as its single brick thick, and in the bed room the roof of the bay is flat with lead flashing and I suspect no insulation)

then the rest are all from Wickes, fitted with fins:

1100 x 600 single x2
800 x 400 single
800 x 600 double
1400 x 600 single
1600 x 600 single

The system has a WILO Gold R550 pump fitted, pumping downwards.

The problem is the pump is silent when cold, but as soon as the water starts to heats and gets above 45 deg it sounds like it is cavitating, and on initial start up you sometimes get a sloshy-slooush sound too.

I have tried the system on speed 1, but this just causes the boiler to cut out due to over heating..

it was running on speed 2 when we moved in, and has been for the last year, however when I mentioned to a friend that I seem to keep getting air in the bathroom and back bed room rads and described my noise to him he said I was getting cavitation and to turn the pump up to see if that helps.

I also filled the system with Feronox that he reccomended, (the system appears to be clear as when changing the rads last year we drained it and refilled it, but at the time I did not put any addative in as I was planning on doing the other 2 rads shortly after, however that plan got put on hold)

I tried speed 3 but it still made the noise...just higher pitched.

I have noticed though that the hall rad which is the long one gets hot on the inlet, and along the top, but the outlet never gets above luke warm, I tried to balance the system but with limited success.

any thoughts on what to do? the boiler temp is set to about 53 deg, it normally goes up to about 57deg cuts out, cools down to mid 40s then clicks back in again. (the heating is not controlled by a room thermostat, but I will start another post for that shambles!)

cheers

Karl

 

[SimonJohns]

Sounds like there is alot of restriction in the system. I would reccomened from what you are saying that its time for a new boiler and a conversion to a sealed system

 

[M7R]

the boilers only 4 years old, and I am lead to be belive it is a top notch boiler.

 

[SimonJohns]

Right.

First of all you shouldn't have a boiler that locks out at 50'c +
Sounds like you have air in the system thou

How full is your f and e?
Are all valves fully open on pump. And others that should be fully open

Do you have trv's

 

[SimonJohns]

Even pictures of pump arrangement and pipework would be good

 

[M7R]

the boiler will go higher than 50 deg, last winter when it was sub 0 for a few weeks and we had the old 60s rads it was running at 70 deg, I have turned it down as now we have the new rads the house does get warm enough, we have TRV's on every rad (apart from the hall one) these are set to 20deg at the mo (we don't have a main stat - see here for why http://www.ukplumbersforums.co.uk/c...on-digistat-scr-appears-have-been-passed.html )

what do you mean by "how full is your f and e"? (sorry I am more than happy building car engines and doing DIY etc, but I am only just starting out on my understanding of the in's and out's of central heating systems)

I will double check the pump valves now,

cheers

Karl

 

[M7R]

Boiler install

feed and return

Pipes down by the water tank

Pipes down from pump and into 3 way valve

Pipes going under floor to rads and hot water feed to kitchen

Checked the valves, and both on the pump are fully open.

 

[diamondgas]

Dumtedum dum deee... de dummm te dummm dummm!!! LOL

Guess this post is dead? Excuse me op! Did you have your system flushed out B4 installing? Not that its an issue but can rule out afew

 

[M7R]

I have done some calcs and the smallest boiler in my range is 25Kw, all my rads (inc the new ones planned) only add up to 11Kw in total.

I don't know if the system was flushed, but I did drain and re fill a couple of times when we changed the rads and a couple of valves.

I am sure it is cavatation in the pump due to it being quiet at lower temps, so I just need to find out why / how to fix it? (different pump? or different location?)

 

[SimonJohns]

I have replied a couple of times to this, but it says my posts are waiting for an admin to approve them,

there should be pics etc being posted when they are approved.

I have done some calcs and the smallest boiler in my range is 25Kw, all my rads (inc the new ones planned) only add up to 11Kw in total.

I don't know if the system was flushed, but I did drain and re fill a couple of times when we changed the rads and a couple of valves.

I am sure it is cavatation in the pump due to it being quiet at lower temps, so I just need to find out why / how to fix it? (different pump? or different location?)

try taking the pump apart and inspecting the impellor

 

[kimbo]

It would appear that you are getting air pulled in to the system when the pump starts up, the pump should not be on setting 3, usually 1 or 2. The vent and the feed pipe should be before the pump ideally no more than 150mm apart otherwise on start up it can draw air in from the vent. A photo of the pipes would help.

 

[diamondgas]

Good luck !

However if you'd like to talk heating system design flow rates and temo diff f&r expectations, system requirements etc then you may be in luck on this site! Cavitation is for engineering ipellor design folk IMHO! A pump circulats water around heating systems upto and including 80 degC. Cavitation is a bi product of poor design IMHO

 

[dancinplumba]

do you have a by pass ? if not and your trvs shut down ther is a lot of resistance for your pump to overcome this could poss cause noise imo

 

[M7R]

there are photos up now, on page 1, I can try and get pics from in the loft tomorrow as the pipes go straight out of the boiler, in to the loft and then appear to come back down as shown in the pics with the pump on the feed side.

 

[M7R]

taken the pump out of the loop today and taken it apart, theres a bit of black crud in there (which is a bit odd as when we drained the system it was pretty clear, although some rads did have some black crud in, and now when ever you bleed a rad its pretty clear bar a slight pale yellow tint)

should there be play in and out of the impellor? as mine moves in and out about 1 - 2mm, the bearing doesnt appear to have colapsed as In can not rock it up and down.

Karl

 

[Puddle]

You will have a bit of play in the pump,not a problem,clean it out and replace,maybe time for the magnet test,get a magnet and check the pipework above pump and boiler ,especially where feed and vent pipework tee into system,see if any build up of corrosion there causing restriction

Might be an idea to put some mild sentinel cleaner in system and let it run for a week or so

 

[M7R]

well went to screwfix as I was getting a few other bits anyways and picked up a wilo smart A pump as I thought even if it doesnt work it will at least save me a couple of quid over its life time and I will have rules that out.

tried to fully bleed the pump but on start up it was noisey, left it running with cold water and after a min it went silent! gave it 15 mins then turned the heat up, sat now at 60deg+ water temp and I have a small amount of tricking water noise, but no where near as much as before! (if I shut the door I can only just about hear it in the bathroom but not on the landing or our room at the front of the house and through 2 doors (with solid brick walls! got to love old houses!)

I will still have a look in the loft at the weekend at the feed and vent etc, any photos of what I should be looking at in a correct install?

also anything else worth adding? I have feronox in there, but I know the header tanks a bit scuzzy on the walls (the water is pretty clean though)

 

[M7R]

spoke too soon :angry_smile: went down stairs for tea, could hear the pump in the pipes, but no ad bad, then it quietened down, but noticed the rads werent red hot, went back up stairs and the boiler had thermal cut out, knocked the temp down a smidge, hit reset and the pumps noisey again! bugger!

next plan of attack?

 

[SimonJohns]

get a gsr

 

[diamondgas]

Do you have a separate feed and vent pipe or is it a combined feed and vent pipe? Is that the loft space directly above the boiler? how much head of water is there from the flow pipe in the loft to the water level in the f&e tank? Lot of questions i know but it sounds like you are drawing in air, as mentioned, Which will stop circulation in its tracks and then the boiler will overheat! A bit more understanding of the lay out above the boiler would be of benefit

A downward pointing pump is not the best by the way! They'll always struggle to clear air!!

 

[kimbo]

You have to find the root cause of the problem a new pump would not sort it out. In the installation of the pumps paprwork it does say it can be pumping downwards but as diamondgas says it is better pumping up as it tends to naturally get rid of the air trapped. Also the height of the pump from the header tank should be a minimum of 1/3rd of its head and the feed and vent needs sorting as previously mentioned.

 

[M7R]

get a gsr

GSR??

Do you have a separate feed and vent pipe or is it a combined feed and vent pipe? Is that the loft space directly above the boiler? how much head of water is there from the flow pipe in the loft to the water level in the f&e tank? Lot of questions i know but it sounds like you are drawing in air, as mentioned, Which will stop circulation in its tracks and then the boiler will overheat! A bit more understanding of the lay out above the boiler would be of benefit

A downward pointing pump is not the best by the way! They'll always struggle to clear air!!

I have no idea why they have put the pump facing down, for me it seems daft as air will always rise in water... so it will just get stuck in the pump fighting against the slow of water.

here are pics of the pipe work in the loft, if you need any more pics let me know as I have tried to get the best pics I can.

it appears there is some kind of automatic bleed valve I guess standing up, however this appears to be on the return pipe and not the feed pipe.

there are 2 pipes Tee'd off the hot pipe, one goes up and one goes down, they are Tee'd off next to each other, the one that goes down goes to the bottom of the header tank, and the one that goes up goes to the top of the header tank (i think thats how I remember it, I should have tanke a pad and pen and drawn the lay out with notes if I am honest... ill go back up later)

 

[diamondgas]

See if I have fathomed these out correctly Hopefully you can make out the labelling I've wrote.

If there's a separate feed and vent, which sounds like thats what you're describing, it could be possible to fit an air separator on the heating flow and combine the feed and vent pipes to overcome any possibility of your issue being 'air'. Take this as just a suggestion though as without first hand knowledge I wouldn't commit to it being a cure! Combining the feed and vent will certainly alleviate the possibility of air being drawn in or 'surging' occurring

 

[M7R]

yep that looks to be right, with the return having some kind of filler / bleed fitted? (the tops screwed on tight, I moved it with some pliers but it started to weep a drop so I chickedned out and did it back up)

 

[diamondgas]

yep that looks to be right, with the return having some kind of filler / bleed fitted? (the tops screwed on tight, I moved it with some pliers but it started to weep a drop so I chickedned out and did it back up)

If the pipes are as I'v perceived then the vent and feed are decently placed and the vent should dicipate any air before getting close to the pump! However as said before, a combined f&v would eliminate any 'drawing in' issues!

IF your cold feed is blocked then you could have air drawn down the vent! I'll emphasise IF!

Seeing the layout in the loft though I'd be back down stairs wondering WTF!!!! lol

 

[M7R]

The feed is working as when I added the fernox to the system I bailed out header then opened a bleed valve to dran some more out and the level was dropping,

The service guy is coming monday so he says he will see what's happening and how to fix it, earlier this eve the pump was running silent at 60degs!

 

[diamondgas]

How about the downstairs rads? lol

We're still compramised with circulation if the rooms you want heated are cold yeh?

 

[M7R]

down stairs rads get hot, take a bit longer (a while longer in a few cases) but they do atleast get hot and dont seem to collect air.

the only one that doesnt work quite right is the big hall one like I said on my OP, as the inlet red hot and the tops hot but the outlets cold, even after a few hours as is an area around the outlet at the bottom. the valve is wide open though ( 2 new valves fitted last year when we swapped the rad) and I know its open as a couple of weeks ago I closed the inlet and opened the bleed to try and see if the rad would allow the warm water in backwards... not really even though I did drain about 1.5L from the rad in the end)

 

[jhon lennon]

you need a new pump the one that's in is worn that's why the hotter it gets the nosier it becomes the cool hall rad is due to balancing and to do it right is not the dark arts just time consuming good luck let us know how you get on

 

[Billy Bob Bob]

M7R is your house a bungerlow?

 

[M7R]

as i have said further up I have just changed the pump for brand spanking new smart pump, and I was still having the same problem.. it seems to be quieter for longer now but was still making a noise, I will keep an eye on it and see if it gets better or worse.

and no not a bunga, a 1950s semi house.

I have tried to balance the rads, but it seemed to make no odds, however that was with a noisey pump which wont be 100% efficent, so once the pump is sorted I will give it another go.

 

[diamondgas]

What happens when the hot water is satisfied? Does the heating get any hotter, the rad that's poor does that get hotter on heating only?

I noticed you have ballancing valve on the hot water return, is that fully open or has it been turned back? Is there a bypass, it looks like there's a pipe taken off before the diverter, is that the bypass? If so is that fully open, closed off or even automatic?

You're describing a definite circulation/ballance issue. Have you/can you check the problem radiator for a restriction internaly?

Just a few more things to try for you :lol:

 

[M7R]

What happens when the hot water is satisfied? Does the heating get any hotter, the rad that's poor does that get hotter on heating only?:lol:

it doesn't seem to make any odds, and never really sure when the hot waters satisfied if I am honest...however if I run just heating only the hall rad still seems to hot one end cold on the outlet and near it..but I will keep an eye on it and see what happens when running CH only.

I have just been and had a play though, both HW and CH were on, clicked to turn HW off and it made no change to the noise (pump was pretty much silent bar the odd tiny gurgle even at 50+ deg) set it to HW only and then it made a gurgle and I could hear what sounded like air rising, then the pump went noisey, and about 30 seconds later the boiler clicked out) then set the controls back to both HW and CH, but it was still a bit noisey.. so now got it on just CH and seeing if it quietens down again.

I noticed you have ballancing valve on the hot water return, is that fully open or has it been turned back?

just checked it was wide open, I am guessing it should be closed a bit to help send more heat round the CH system? closed it a little now but when it got too shut it was making running water noises a bit.

Is there a bypass, it looks like there's a pipe taken off before the diverter, is that the bypass? If so is that fully open, closed off or even automatic?

where abouts am I looking? and I will go and check?

You're describing a definite circulation/ballance issue. Have you/can you check the problem radiator for a restriction internaly?

nope not checked it, however its just a year old, and if I close the inlet I can bleed the rad via the outlet easily enough.

 

[diamondgas]

just checked it was wide open, I am guessing it should be closed a bit to help send more heat round the CH system? closed it a little now but when it got too shut it was making running water noises a bit.

Try cracking to 1/4 open as a start point. You've got to guarantee enough flow on h/w only through the boiler otherwise it'll trip on o/heat.

where abouts am I looking? and I will go and check?

There seemed to be a 15mm pipe teed off after the pump and before the diverter valve, it carries on down from the pump and seems to go under the floorboards.

What you'll fiind when both hot water and heating are calling is that the priority flow will travel through the hot water circuit unless you restrict the flow via the ballancing valve!.. Idealy you are looking for 11 deg C diff between the F&R pipes at the cylinder from cold! To small a difference tends to indicate the flow is fast, especially if the cylinder of water is cold!

 

[Nostrum]

A good way to test if your drawing air, get a 22mm speed fit cap end. Let system cool completely, vent all the rads, the vent in the loft (the one which weeped water so you ran away) stick the 22mm cap on the vent pipe which goes over the F&E tank in the loft. Pump speed on 2 and let it run for an hour.

This is a TEMPORARY test only, if it stops the problem you have an issue with your vent configuration so call a professional in. The system will work like a combined cold feed and vent but only using the 15mm cold feed so it is not satisfactory to leave it like this for any lengthy period of time.

You could stand up there with a jar full of water but this is a bit easier to do.

It sounds like you have multiple problems with the install, balancing and air ingress

Sam