Gurgling central heating leading to half empty radiators

[parksy]

Hi all

I have a problem with my central heating system. It has been the same for the last 3 years when I moved in.

There is air (a lot - about 1/2 radiator) in 3 of the upstairs radiators. I can bleed most of it out, but not all. I’ve tried bleeding with the pump on and off. I’ve also turned off the individual outlet valves on each rad to get more pressure in the push the air out (returning them to normal afterwards). Sometimes there even seems to be negative pressure in the rads – hissing noise but you can’t feel the usual outflow of air. So there seems to be something of a lack of pressure in the system. The header/expansion tank is full, although I can feel some sludge at the bottom of it. The pump seems to be working ok, and I’ve tried it at all 3 speed settings. I also tried bleeding the pump (screw in centre) but didn’t get anything.
Having got most of the air out of the rads, the next morning when the system comes on, there is the most almighty gurgling in the system waking up the entire house for a good 30 minutes. The gurgling seems to be from the inlets of the radiators affected, but sounds like it may be in the loft too (where the expansion tank is). I tried to place the loft sounds exactly, and they actually seem to be from the cold water tank rather than the expansion tank.
After a few days of leaving the system alone, it settles down and is quiet, albeit with half-full (and thus not hot enough) radiators.
If I bleed the rads again, I get the morning noise problem again.

Is it possible that the system is somehow syphoning water back into the header tank? If so how do I stop this?

Thank you for any help.
Chris

 

[HarrogateGas]

Sounds like your cold feed is blocked or partially blocked. Its usually ay the point where it tee's into the system.

 

[parksy]

That would make sense. Thanks for such quick reply.

How should I go about trying to clear the blockage? Can I use mains pressure to try to clear the header pipe from above? What if that doesn't shift it?

 

[ChrisRoberts]

U'll need to cut the cold feed pipe just above where it joins the main heating pipe. U need to empty the exp tank or block the cold feed otherwise U'll get wet. I doubt mains pressure will clear it. I just had to drill a blocked cold feed. Good Luck.
I once went to a blocked 28mm cold feed on a 42mm heating pipe. Is this a record? Oh and I got soaked on that one, which was nice.

 

[parksy]

Hi Chris

That sounds relatively straightforward - I'll get the towels ready! I don't envy your 28/42mm version!! Where are trained diving rats when you need them?!!

Thanks for the advice.
Chris

 

[Soggy_weetabix]

And there was me so proud of having to drill out a 22mm cold feed. You have really **** on duvet now!