Help with a mystery gate valve....

[giw12]

Hi there

I'm in my first winter in a new house and I've spent the last few weeks trying to figure out how the CH system works (open vent F&E, Potterton Osprey), particularly as the rads weren't getting as hot as I thought they should.

I'm no expert but in discussion with a few friends I've managed to get a pretty good idea of how it all hangs together. Also managed to improve the balancing of the rads (thanks to my research on here) so the heat distribution is much better.

The one thing no one can figure out is the purpose of one of the gate valves. Rather than trying to describe it I've got a a couple of pics of the set up.

http://s251.photobucket.com/albums/gg301/giw121/

The mystery valve is the one just above the 'Return' text in the first pic. It was fully open originally but all this seemed to be doing was letting half the pumped flow go straight back to the boiler (the return to the boiler is just below the valve and goes through the ply). I closed it (but not completely) and the rads felt hotter and the boiler seemed to start and stop less often than it used to.

However, the prob I have now is that when the hall thermostat reaches temp and switches the central heating off (remembering that it's still officially on as per the boiler programmer) then there's a loud whine that seems to come from the pump. If I up the thermo a few degrees past the click then the noise goes.

Sorry to bang on but I wanted to make sure there's enough info.

Please can someone tell me what this valve does and whether it should be open/closed/in between.

Many thanks
Gary

 

[Rob]

Its a by-pass. When the two motor valves close the boiler presumabley has a pump over run which keeps the pump going to cool the boiler down after eveything else has turned off. It needs the bypass as a permanent return path.

Your right it shouldn't be fully open but needs to open enough to provide sufficient flow to dissipate the heat in the boiler.

Nowadays we use auto bypasses which ONLY open when the motor valves close.

Open it enough so that there is no 'whine' from the pump. You'll soon burn out the pump if you dont.

 

[giw12]

Thanks for the info Rob.

One question....if the CH is still on as per the programmer but is up to thermostat temp then wouldn't the motorised valves remain open?

 

[twgas]

programmer and thermostat are wired in series so if either one turns off the MV will close.

and it looks like a water leak by your yellow pump, or have you just bled it?

 

[giw12]

programmer and thermostat are wired in series so if either one turns off the MV will close.

and it looks like a water leak by your yellow pump, or have you just bled it?

Thanks..makes perfect sense now.

The mark under the yellow pump is a stain and is bone dry.

 

[bengasman]

Replace the gatevalve with what is called: automatic bypass, it will drastically improve the performance of your system, unless the gatevalve is shut in which case it will drastically improve your safety.

 

[giw12]

Sounds like a very good idea! Could it be directly swapped (the boiler is 2 floors below) or is there a better place to site the auto bypass?

Thanks

 

[bengasman]

Ideally it has as much pipe to and from the boiler as possible, in reality I would not change the location unless very easy to do.
By the way, it does need tuning when you put one in.

 

[giw12]

How much to supply and fit would you reckon?

 

[bengasman]

About 30 quid for a good bypass. Fitting depends a bit on how long it takes to drain and refill the system and whether or not there are airlocks to get rid off. I’d say an hour but it could well be longer. Times the local rate. And a litre of inhibitor, very important, and no no-name cheapo.