Devices on boiler return pipe

[Makeitgo]

Hi all, I'm new to the forum and to fixing CH problems as well.

I've got a couple of questions and was wondering if anyone could shed some light.

The set up is a follows:
The installation is 30 years old and has a hotchpotch of Stelrad radiators. It's in a flat and is an open vented system.
- Cold water tank and F&E tank in loft, each has own respective vent pipe
- Ideal Icos HE18 boiler is a floor below the loft (boiler was installed 2009)
- Water cylinder, circ pump and 3 way valve is about 3 feet below boiler
- 3 rads on same floor as water cylinder and one rad a floor below this level

System has been making occasional low level clunks since it's installation 4 years ago. It got worse recently,so I thought it might be hot spots, as I tested the F&E cold feed and vent and didn't find a blockage in either. I then started to make all rad valves and bleed vents usable before various water draining and desludging routines etc.

I half drained water from lowest rad, so I could replace a bleed valve on a higher level rad. On completion, I turned on mains to F&E tank and only about a gallon of water seems to have gone down the cold F&E feed pipe (air in system I guessed).

So, then I was looking at correct order of rad bleeding, refilling etc, when I discovered something I think is a bit strange. At the top of the boiler immediately (3" from boiler) there are two in-line devices on its return pipe:
- What looks like a drain cock (be interested to know when to use it)
- What looks like an end cap, but with a straight knurled thumbscrew on it that is turnable

Thing is that I've never touched them and they were both OPEN i.e. not fully turned off to the right when I found them! I'm thinking that they may have been introducing air into the system for four years, but I don't know. I feel like turning both off, but don't know if the second one is an overpressure safety device and not sure if I should touch it.

I have attached a picture and was wondering if someone could tell me what they are and also anything else that might be useful for me to know.

Thanks a lot in advance guys

 

[Fluffster]

You are correct one is a drain cock and the other is a manual air vent which you simply open to release the air and tighten by hand to close.

Pete

 

[Makeitgo]

You are correct one is a drain cock and the other is a manual air vent which you simply open to release the air and tighten by hand to close.

Pete

Thanks Pete
So are you saying that because they have been open there might have been air going into the system (incorrectly) for ages and that I'm safe to stop this by turning both of these off? I don't know if I successfully uploaded the photo. Did you see the photo?

Thanks

Chris

Edited to add pic:

Untitled

• Makeitgo
• 16 Nov 2013
• 1

 

[Makeitgo]

OK, thanks very much for your help Pete. I made sure both the drain cock and the manual air vent was closed, got the system up again with valves open only on two rads and have been bleeding them, getting a good result.

What baffles me though, is that when the drain cock and vent were open (unintentionally) all this time, why wasn't there water Pi**ing out of them?

Bonus points anyone?

 

[JohnD]

Blocked with hardened sediment, perhaps. If you touch them they will probably leak so have replacements handy.

When you are working on an old open vented system it is worth giving it a simple DIY chemical clean. Sentinel X400 is mild and non-acidic. There are faster and more aggressive chemicals available. Bale out the mud from the F&E and sponge it clean first.

 

[Makeitgo]

Thanks JohnD
Oh yeah, hadn't thought of sediment in them as they are so close to the boiler, thanks for the tip. I was also wondering about what cleaner to use - and that sounds good to me.

The water I've had out so far has generally been various shades of wee colour (whilst not eating beetroot) so I'm assuming that when the boiler was fitted, they did a no-power flush and added some inhibitor.

Cheers

Chris