C plan system airlock

samag

samag

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Hi guys, we moved into a place last Dec with an old Grant Euroflame oil boiler with 4 pipes, one set with a Grundfos pump on it and the other set running upstairs to a HW cylinder. We've never been able to get HW generated from the boiler for a sustained period, the water doesn't seem to flow that side at all.

Early this year I was having to regularly bleed the pump (which was 20 years old+) as the CH would get stuck and only come back after bleeding air from the old pump. I figured the pump was on its way out. A month ago I went to switch it on after it being off all summer and it wouldn't budge at all so we fitted a new UPS3 and it worked faultlessly for 2 weeks.

Then I partially drained the system down to add inhibitor, topped back up and since then after ~20mins of boiler+pump being on (doesn't happen if just the pump is running without the boiler.. even if the CH water is still running hot) there's a wooshing/gurgling noise and the pump will sound strained and the rads just cut off, no circulation. The pump goes dead quiet but still struggling doing something.

I've bled all the rads and there's no more air that I can get out, after getting some initially after the system was topped back up. When the block happens I have to turn the pump off and on for 5-10mins which is noisy (like bubbles going through it) and gets something moving and then the system will work for 10-20mins again. I've tried to bleed the rads closest to the boiler after the system is unblocked though, can't get anything out of them except water (which is clear, no sludge coming out). It's odd that the system was working just fine for weeks until I drained and topped it up.

Anyone with any similar issues in the past? Been wracking my brain for weeks to figure this out. Cheers.
 
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Apologies for the amount of text.. can try to slim it down but hard to fit all the info in.
 
partial drain down , did the header tank empty when draining and has it refilled ,
if so then airlock in the HW gravity circuit you could try boiling it up by just having the hot water on and removing the thermostat phial it will thump and bang a bit but should clear the airlock . may take a couple of attempts
 
yes exactly.

This is what I was hoping might have happened (as it should be fixable myself), I was going to take the insulation off the tank to see if I could bleed the air out the coil. I have done what you describe before, running boiler on HW until the bangs start- I was doing it last winter to get HW working off the boiler for a bit. So that's what it was doing, clearing an airlock - thanks that's useful to know. It would clear the HW side for a week and then get jammed again, so was having to do it once a week and was worried it would end badly (pipes breaking) so stopped doing it and went back to immersion. Any idea why this side would keep airlocking?
 
Providing cold feed is clear and its filling which it sounds like it is , it may just be down to a poor pipe run design and with the age of system the pipe have accumulated some crap in them
 
ok, going to try flushing system with x800 for a few days this weekend (clearing airlock after adding it in so that whole system circulates)

Cheers
 
blimey that could be the reason our old pump went out over summer then, leftover x800 from early this year (didnt work of course because the airlock introduced via header tank would've prevented it circulating around the problem HW side)
 
You say it's a C plan - can you see the 2 port valve on the return pipe from the cylinder ?
 
I say c plan like I know what I'm talking about, it's just the only one I've seen that matches our 2x2 pipe setup. Our setup matches c plan apart from I am not sure we have a 2 port valve, just a knob that can be adjusted on the return(?), See image of our cylinder with the boiler pipes circled. Can't find anywhere I can bleed trapped air from it, so gonna have to keep on blasting it out via running boiler on HW only.
IMG-20221103-WA0002.jpg
 
samag said:
I say c plan like I know what I'm talking about, it's just the only one I've seen that matches our 2x2 pipe setup. Our setup matches c plan apart from I am not sure we have a 2 port valve, just a knob that can be adjusted on the return(?), See image of our cylinder with the boiler pipes circled. Can't find anywhere I can bleed trapped air from it, so gonna have to keep on blasting it out via running boiler on HW only.
View attachment 284575
Click to expand...
Take the head off that thermostat make sure the pin pushes in and out on the valve body
 
The coil should be self venting, assuming valve is open sufficiently. The pipe going up from the Tee on the top of the flow pipe is the vent, should go up and loop over the F&E cistern. I don't think the issue is air, is more likely sludge.

Given the cylinder is an antique, it may be well worth biting the bullet and upgrading the cylinder, system and controls.
 
samag said:
blimey that could be the reason our old pump went out over summer then, leftover x800 from early this year (didnt work of course because the airlock introduced via header tank would've prevented it circulating around the problem HW side)
Click to expand...
That is exactly what happened to your pump do not use x800
 
If your mump is easily accessible, try turning it round the wrong way and run for 30 mins or so, that sometimes clears air locks, also when the pump was changed was it definately fitted the correct way round ?
 
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