Airlocks in HW/banging mid position valve

[PeteH]

Please help, at end of my tether System is traditional Y plan, Gloworm 40FF boiler, Grundfos pumped primary circuit for rads/immersion coil, gravity fed HW by loft tank. New boiler fitted Sep 04, great for 5 weeks then HW not heated, only CH. Company called back, said Honeywell mid position valve faulty - problems ever since they replaced it: Pipes howled/rads bubbled - came back month later, fixed by opening last rad valve. Since then one very loud metallic bang comes from valve and pipes between it/boiler, only when HW program starts, not CH. No joy getting them back to check this - guy had problems wiring it up. Any idea what problem is? Even worse, only since valve replaced we keep getting airlocks in all HW system every few weeks - all HW taps gurgle, slow to trickle then stop. They did come back to drain/refill system 5/1/05 & Ok till last night, blocked again no HW! Have checked both loft tanks filling OK/pipes lagged/not frozen. Any suggestion what problem is would be much appreciated! Could it be scaled pipes? Sorry if duplicate post, last one didn't seem to send.

 

[ChrisR]

Tap hw isn't connected to boiler hw so only source of bubbles etc in tap would come if the hw is stored too HOT - check the thermostat on the cylinder.

Put hw on with ch off. Make sure hw stat is calling for heat. MOst commonly, there will be a lever on the end of the motorised valve resting n the HW position. You can tell that by trying to move the lever away from its end stop. If you feel a spring holding the lever back, that's right.

That'll do for now..

 

[PeteH]

Many thanks for the reply. The cylinder stat is new, having been replaced at the same time as the boiler. It's only set on 45 degrees and I have previously checked it's operation as OK, although my other half did get a bit burnt by the water last night before the airlock set in so perhaps that's a problem - will check when we get hot water flowing again!

As you point out, the HW is on a separate circuit to the boiler so any air in that part of the system shouldn't affect it. I can't understand where the HW airlocks keep coming from and neither can the company that fitted the boiler/valve. All I know is they are driving me nuts and only started when the new mid position valve was fitted. I live in a very hard water area and the pipework is still original (18 years old) - could limescale in the pipes be the problem?

I will check out your tip regarding the mid position valve. Cheers.

 

[ChrisR]

Cylinder stats have to be clamped very hard to clean copper to work. Scalding water means it isn't working!

Check your electric immersion heater isn't switched on, if you have one.