How to bleed sealed system

[vernonr]

Looking at a friend's system yesterday. The boiler is refusing to fire and showing a fault code indicating no water flow. The pressure vessel gauge shows a pressure of 1 bar.

I concluded the schematic was roughly as shown here

I'm concerned that

• the pressure vessel gauge could still register pressure correctly even if there are airlocks in the system.
• there appears to be no air vent at the highest point on the boiler outflow side..

What would people advising doing first ?
What else would you want to find out?
If we can ensure the boiler fires and heat the hot water tank; then we can move on to sorting out the central heating circuit after that.
Thanks in anticipation.

 

[oz-plumber]

What boiler is is and what is the fault code?
Depending on the boiler and the fault code it is showing could depend on what is wrong.

If the boiler is not kettling, then i doubt it would be the pump.
Could be a faulty sensor or the like.

More info needed

 

[vernonr]

What boiler is is and what is the fault code?
Depending on the boiler and the fault code it is showing could depend on what is wrong.

If the boiler is not kettling, then i doubt it would be the pump.
Could be a faulty sensor or the like.

More info needed

It's an ideal logic 18 - fault code F d - no water flow... but the water flow sensor has just been replaced. I don't think the boiler can be "kettling" given the pipework is cold - and the boiler won't fire. What about blockage/air locks - how would you eliminate that possibility? Pump appears to be operating normally..

 

[Chuck]

It's an ideal logic 18 - fault code F d - no water flow... but the water flow sensor has just been replaced. I don't think the boiler can be "kettling" given the pipework is cold - and the boiler won't fire. What about blockage/air locks - how would you eliminate that possibility? Pump appears to be operating normally..

Try bleeding the pump by slackening the big (5 pence coin size) 'screw' cover over the bearing.

Stick your ear on a radiator and see if you can hear water flowing when the pump is running. If you adjust the TRV while doing this you'll be able to hear turbulence developing as the valve shuts.

If the water is circulating you need to get a registered gas engineer to investigate the boiler. A faulty boiler is way more likely than a previously working system spontaneously developing an airlock.

 

[vernonr]

Try bleeding the pump by slackening the big (5 pence coin size) 'screw' cover over the bearing.

Stick your ear on a radiator and see if you can hear water flowing when the pump is running. If you adjust the TRV while doing this you'll be able to hear turbulence developing as the valve shuts.

If the water is circulating you need to get a registered gas engineer to investigate the boiler. A faulty boiler is way more likely than a previously working system spontaneously developing an airlock.

Thanks Chuck for the ideas about diagnosing water flow... How would you hear if water flow was actually occurring through the boiler pipework and hot water tank. Is there anything one could connect - e.g. to a magnaflow filter connectors to view?

Agree that a previously working system is unlikely to spontaneously develop an airlock. But after failure if the system was partially drained that could
I believe the sequence of events was

1. Heating fails.
2. Suspect boiler - so boiler gets serviced - boiler parts renewed - which involves partial drain ...
3. Reconnection - but system bleed was never verifiably complete... bad pipework etc. partially to blame..Lack of operation blamed on pipework etc.
4. system converted from traditional to sealed - again without verifiable bleed or circulation check of system..

Pump operates fine, varies speed - slight vibration felt - but no big 5 pence to bleed from this particular Grundfos pump.

Thanks

 

[Chuck]

Thanks Chuck for the ideas about diagnosing water flow... How would you hear if water flow was actually occurring through the boiler pipework and hot water tank. Is there anything one could connect - e.g. to a magnaflow filter connectors to view?

You haven't mentioned checking the zone valves are operating.

The fact a pump is humming is not proof it is pumping; the impeller may have jammed, for example.

I'd expect you to be able to hear the water flowing through the filter. Use a piece of dowel rod as a 'listening stick' to help. Practice on a pipe you know has flow in it, e.g. feeding a running tap, to get an idea of how sensitive the method is. If no joy, then let about 50 ml of air into the filter I'd expect you to hear a distinct trickling sound. If you want to be absolutely belt-and-braces sure, you could substitute the magna flow for a 'sight glass flow indicator'.

 

[vernonr]

Thanks Chuck,
There's a Y valve rather than 2 zone valves. It is operating. I doubt the impeller has jammed as the pump hum changes as I change the requested speed on the pump.
We'll investigate the flow with the dowel and/or the flow indicator. Any recommendations for a make / where to get a suitable 'sight glass flow indicator from'? They seem to be widely different specs & prices...
Thanks

 

[oz-plumber]

It could be an situation where the impeller has broken off from the shaft.
So the shaft may be spinning, but the impeller is sitting still - not pumping water.

 

[vernonr]

It could be an situation where the impeller has broken off from the shaft.
So the shaft may be spinning, but the impeller is sitting still - not pumping water.

Hi oz-plumber.
I can see why this would prevent water circulation. But it seems unlikely and begs other questions..
What would have caused the shaft/impeller to jam or break?
Do Grundfos pumps suffer often from this?
Would one see it easily if the pump was removed?
Thanks

 

[oz-plumber]

Years of experience?

You claim the pump motor operates on all speeds but the boiler has no flow.
If the system was operating and then stopped, due to no flow & the flow sensor was changed, I would hazard a guess that the pump may be the problem.

As for the many issues there are with pumps, impellers broken from the shaft is a rare one, but it suits what you describe.

Remove the pump from the pipework and fire the pump. you will be able to see if the impeller is spinning

 

[ShaunCorbs]

Years of experience?

You claim the pump motor operates on all speeds but the boiler has no flow.
If the system was operating and then stopped, due to no flow & the flow sensor was changed, I would hazard a guess that the pump may be the problem.

As for the many issues there are with pumps, impellers broken from the shaft is a rare one, but it suits what you describe.

Remove the pump from the pipework and fire the pump. you will be able to see if the impeller is spinning

Or as most ups3 the impella gets stuck