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

 

[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?