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

 

[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

 

[M7R]

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

Okay I will have a look at this, I will let the vent in the loft bleed just encase there is air in there.

I am guessing to let it run for a hour with the boiler on and at normal temp (about 55 -60 deg or so).

The lad that came and serviced the boiler yesterday (it got a clean bill of health so I know thats good all he had to do with give it a quick hoover out but that was it) he suggested another fix would be converting the system to pressurised. he said it shouldn't cost that much as we would need a new water cylinder, and the pipe work in the loft changinging a little, plus a cold feed adding inot the system (which is easy as there is a cold feed going into the loft for the tanks running right next to the boiler).

is there any down side to going pressurised? and will till most likely fix my probs? as getting rid of the header tank in the loft would be a bonus as we plan on doing a loft conversion in a couple of years time.

 

[diamondgas]

Pressurising comes with potential problems increasing the chance of water leaks. A typical pressurised system is set to 1bar. That's the equivalent of raising your header tank to 10m high. Added to that the pressure is allowed to get to 3bar before safety devices cut in then you're system is going to be introduced to a great deal more pressure than it is at the moment use to! There are other potential problems too but the major one is will your system stand the increased pressure. Personally combining the feed and vent does just as good a job as 'sealing' it IMHO

 

[M7R]

I think most of the pipe work is new, but then again I will try the combined vent and feed and see what happens (also thats cheaper).

(I was playing with trying to balance the hot water tank last night, and setting the thermostat on the tank to the right temp) and at one point there was a massive glug of air rising from within the tank and seemed to go up into the loft!

 

[diamondgas]

I think most of the pipe work is new, but then again I will try the combined vent and feed and see what happens (also thats cheaper).

(I was playing with trying to balance the hot water tank last night, and setting the thermostat on the tank to the right temp) and at one point there was a massive glug of air rising from within the tank and seemed to go up into the loft!

Once the f&v are one the pump can not 'suck' anything but water down the pipe which will eliminate the chance that air is being drawn in from above! The pipe needs to be 22mm minimum but check the mi's to make sure you can do this for your make of boiler. Being a modern one though I doubt it'd be an issue!