New House- Noisy pump on HW

[Jondersmit]

Hi

We've just moved into our new house. We have a standard open central heating system (10 years ols) with a glowworm boiler, standard expansion and header tanks in the loft, central heating cylinder etc (that's about as technical as I get). When we moved in some radiators needed bleeding so that got done pretty quickly.

Basically we have reached the point now where when the CH is on there's no noise and everything is OK. If we then put the HW on as well after about 30 minutes there is the sound of air rushing through the pipes mainly starting at the pump and then going round the rest of the system. From reading posts I assume that the pump is sucking in air from the vent pipe as there are certainly no leaks anywhere else that I can discern. Why would it do this and how do I fix it?

I may well call a plumber out but also just want a general background on the potential problem so i don't get ripped off! thanks.

Any help would be greatly appreciated.

Jon

 

[TicklyT]

Could the tank coil need bleeding?

You may find a bleed valve looking a bit like a car tyre valve cap connected to the pipe coming out the side of the hot water cylinder about half way up.

Well, that worked for me....

 

[Gas2Air]

Is there a gate valve on the return from the cylinder?

 

[Sider]

Hi Jondersmit.

Dont take my word as gospel as I am an ex plumber cowboy (have hung the stirrups up now) but have you tried bleeding the system.

 

[Jondersmit]

I've bled the valve coming out of the cylinder, and the pump and all the cylinders, all to no avail. The only thing I thought it could be now is the mid position valve on the top of the pump, it's got a swtich on the front side of it that is pretty "unattached" to the internals, just seems to flap loosely around. There's a also a selector switch on the side fo "W M C" something like that and that's disappeared right into the body of the valve

- i wondered if this might be faulty- even then I cannot see how it would be causing air to get into the system though.....

 

[Jondersmit]

I actually also meant to write "and i've bled all the radiators, not "cylinders!"...of course there's only one cylinder!

 

[tryitandsee]

May be air is being drawn down the vent pipe, due to the pump being badly placed.

In that case I have found that the pump speed is set to fast and sometimes if you set the pump to a lower speed you reach a compromise, i.e. just enough not to pull air down vent pipe but enough to keep flow to satisfy boiler and rads etc.

Try setting pump at differnt speeds and see if any of them make a difference.

 

[Jondersmit]

Good plan- it does sound like air coming down the vent pipe.

How would i go about turning pump speed down then?
There's a black box stuck to the side of the pump with a wire out the side of it and a turny white knob, i tried turning it and the pump just kept turning off rather than slowing or accelrating in increments-

Any offers on how to turn it up or down (probably a very blonde question) and thanks for your advice so far!

 

[tryitandsee]

Grundfoss 15/50 Selectric 130 Bare Pump
- Ref: 144200

Cater for all domestic systems upto 120,000btu's/hour
Compact size and standard port to port dimensions for easy fitting and for interchange with old pumps.
Three speed motor for energy efficiency and precise system matching.
Further Information
Price: £55.00
(£64.63 inc VAT)

It would appear that you have not got a three speed pump.

Copied this from a internet site. do some research on the pump you have got, it may be to powerful!

 

[Jondersmit]

OK thanks- i'll see what i can do with the pump then, certainly seems to make sense, pump drawing too much and pulling air down the vent pipe.

I'll let you know how it goes.