Pump noise as water temperature rises

[smaplumb]

Hi all

I wonder if anyone could give me some advice?

I had a new (Greenstar 12Ri regular) boiler fitted about a month ago, to an open vent system. At the same time the pump was changed and the new one was installed the wrong way round causing air to get into the system and the pump to be very noisy. This was corrected after running for a few days, however the pump still sounds as if there is air going through it some of the time. When it starts up there is what sounds like a rush of air for a few seconds, but then it runs quietly for 5 to 10 minutes. The noise seems to start as the water temperature rises - I guess at about 45-50 deg C, it happens when the pipework either side of the pump is just too hot to touch. When the boiler goes off and the water cools down a bit the pump quietens down again. I have tried bleeding the pump but no air comes out, just a trickle of water. A small amount of air comes out when I bleed the bathroom rad, but only water from the other rads. Neither the pump speed nor the boiler temperature setting seem to make any difference. The noise seems to be a bit less when both the central heating and hot water are required but I don't need hot water often as I have solar water heating. There seems to plenty of water in the feed tank.

I'm puzzled as to why any air in the system should only make a noise at higher temperatures. Or could the problem be caused by something else?

Many thanks for any suggestions.

 

[craig gas]

may sound a bit obvious but have you checked both pump valves are fully open

 

[jase158]

try draining whole system down, each drop will have to be drained and refilled, this should get rid of trapped air,

 

[smaplumb]

Thanks for the advice. The pump valves may not be fully open, they wouldn't close to isolate the pump so maybe they're broken in a partially closed position. I'll try that and if not then a full drain down ...

 

[tamz]

Straight away i am thinking your systenm has been fitted by someone with little experience. It is not hard to put a pump on facing the right way.

Check the speed setting of the pump. The biggest mistake most inexperienced guys make is setting the speed too high. It should be set to suit the system which is usually at 1 or 2 but very rarely ever at 3.
If the pump is set wrong when it starts it will surge and induce air down the vent. This block of air entrained water will travel around the system and you will hear it every time it passes through the boiler and pump. It makes a bit more noise when it is warmer due to the expansion of the air making it a bigger block of air entrained water.
Get it set correctly and the system balanced to suit.

 

[< 0.004 = :-)]

surprised it fired up with reversed flow before they came back to turn the pump round. couln t have checked the boiler connections or temp differential during commisioning.
just to give you an idea if your installer knows what hes doing, did he mention an auto-bypass valve at all? system might have a bypass fitted allready but more than likely, if it does have a by-pass it's old school, gatevalve with the handle removed. you need an auto-bypass with worcester ri's or guarantee is oot the windae

 

[smaplumb]

Thanks all.

I checked out the valves either side of the pump - one wasn't fully open but now they both seem to be and it hasn't helped. Though there could be a blockage in one of them even though they seem open, that's waiting till I have no other options and have time to drain everything down (or get the installer back).

There's a manual bypass but I think that might be OK? - it's a Y plan layout which according to the manual doesn't have to have a bypass at all. As far as I can tell the motorised valve is working, it seems to cause the right bits of the system to heat up and moves to "hot water only" as its default (which I guess is the equivalent of a bypass?).

I've tried various pump speed settings when the system is running, it doesn't seem to make a lot of difference to the noise but when set at 1 the downstairs rads are quite cool so I've left it at 2. But there is a surge of air when it starts so I'll try starting it up on 1 and see if I can get rid of that.