Finding a blockage in heating pipework

[jaydebruyne]

I think, it sounds like that was the problem during flushing like I said earlier.

Those machines use a higher flow rate and pressure than a CH pump/Circulator.

I am not saying that the Flush has damaged the valve but it could be a possibility.

I would replace it.

It is only my opinion of course and others may well disagree but I would always avoid flushing through the boiler unless it's an older one with a cast iron heat ex.

In combi/modern boilers there are too many small water ways and delicate component parts that are at risk from a high volume, crud filled flushing process.

Just changed the diverter, cleaned out the manifold with the filter on the flow and removed the filter and still the same issue. It's circulating through the boiler via the bypass. In DHW mode it ramps up then back down to 40c where it stays.
In heating mode it ramps up to 78c and then burner goes out, cools down and reignites to bring it back up to temp and cycles through this constantly.

EDIT:
Just spoke to Vaillant, they got me to do a few things and shout out the S codes and they've determined the blockage is def inside the boiler.
I'm gonna check the thermistors on the flow/return when it cools down but he reckons it could be the main hex??? If it were the main hex why would it go through the bypass? Surely it would go through the heating circuit still, no? I know Vaillants are a bit strange...

 

[Chuck]

You said in your first post that the upstairs rads get hot but not the downstairs ones. The boiler is short cycling, presumably because the blockage in the downstairs loop is causing the bypass to open (or it has stuck open). To me these suggest a blockage external to the boiler, specifically in the circuit that serves the downstairs rads. You haven't mentioned the pump sounding noisy (due to pumping against the unbypassed impedance of a blocked HEX) or kettling/banging coming from the boiler, which I'd expect if you have a blocked HEX.

 

[Last Plumber]

Is this the Vaillant with Black rubber hoses?
If it is, Take them off and look inside !
They corrode and decompose to the point were they will block the flow. I have come across what you're describing a few times. If you flushed through the Boiler, it could have removed that black residue from inside those tubes.

 

[jaydebruyne]

You said in your first post that the upstairs rads get hot but not the downstairs ones. The boiler is short cycling, presumably because the blockage in the downstairs loop is causing the bypass to open (or it has stuck open). To me these suggest a blockage external to the boiler, specifically in the circuit that serves the downstairs rads. You haven't mentioned the pump sounding noisy (due to pumping against the unbypassed impedance of a blocked HEX) or kettling/banging coming from the boiler, which I'd expect if you have a blocked HEX.

No kettling, no banging, no noisy pump. I didn't think a blockage in the main hex would cause the bypass to open either.

Is this the Vaillant with Black rubber hoses?
If it is, Take them off and look inside !
They corrode and decompose to the point were they will block the flow. I have come across what you're describing a few times. If you flushed through the Boiler, it could have removed that black residue from inside those tubes.

No its 2 copper pipes for flow/return inside the boiler

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Isn't the bypass part of the pump housing on these boilers? I might be wrong! As I changed the entire housing for the pump too..

 

[Last Plumber]

No kettling, no banging, no noisy pump. I didn't think a blockage in the main hex would cause the bypass to open either.



No its 2 copper pipes for flow/return inside the boiler

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Isn't the bypass part of the pump housing on these boilers? I might be wrong! As I changed the entire housing for the pump too..

There's a small 12-13mm pipe that connects the brass (flow filter housing) block across the back to the bypass screw, which is facing you and is situated to the left of the pump as you look.

 

[jaydebruyne]

There's a small 12-13mm pipe that connects the brass (flow filter housing) block across the back to the bypass screw, which is facing you and is situated to the left of the pump as you look.

Ok .. i think tomorrow I'm going to flush the system and bypass the boiler to see if the blockage is in the pipework or the boiler. At least then I'll know for sure.

 

[jaydebruyne]

There's a small 12-13mm pipe that connects the brass (flow filter housing) block across the back to the bypass screw, which is facing you and is situated to the left of the pump as you look.

To the left of the pump is the diverter which has a brass screw, is that what you mean?

 

[jaydebruyne]

Blockage is def in pipework. Just tried to flush system bypassing the boiler and getting hardly any flow at all. up comes the floor!

 

[Last Plumber]

To the left of the pump is the diverter which has a brass screw, is that what you mean?

Yes, Long thread and circlip, Normally set around the halfway point

 

[jaydebruyne]

Yes, Long thread and circlip, Normally set around the halfway point

Just tried to flush system bypassing boiler, now have no flow at all so blockage is now worse than before. Boiler is fine in DHW but just goes round bypass on heating. What's the best way now of finding the blockage? lol literally exposing entire circuit and checking pipework with a magnet?

 

[ShaunCorbs]

Or putting more pressure in 🙂

 

[jaydebruyne]

Or putting more pressure in 🙂

Via the filing loop? To try and blast the blockage or? Also, I'm I best draining system before going round with a magnet?

 

[Last Plumber]

I wouldn't spend too much time travelling about with a magnet to be honest.
You need to sit down and think through this with a cuppa.
We have not seen the system so it is a bit difficult.

Are you sure that there are no Non return valves or Motorised valves in the pipe work?

How old is the system ?

Not all blockages are ferrous in nature and you said the water wasn't that dirty.

 

[ShaunCorbs]

Doesn't matter if the system is drained to test with the magnet works either way

And would stick 5 bar in it and see what it does

 

[jaydebruyne]

I wouldn't spend too much time travelling about with a magnet to be honest.
You need to sit down and think through this with a cuppa.
We have not seen the system so it is a bit difficult.

Are you sure that there are no Non return valves or Motorised valves in the pipe work?

How old is the system ?

Not all blockages are ferrous in nature and you said the water wasn't that dirty.

It's a combi convert from an old gravity system. Single circuit. Have traced pipes from loft and no sign of any valves unless under floor. Pipework goes up from boiler to 1st floor and comes down to first floor beside the lounge door inside boxing and the disappears under floor.

There are only 2 problem rads, lounge and bedroom. I'm starting with the lounge since this was the one which was first noticed. Then will go on to bedroom and take it fro there. I might check pipework coming down the wall for any valves first though as this is the only pipework I've not checked yet for valves and would be a logical place for an anti gravity valve, no? Or are they nearer to the boiler?

Also when I tried flushing it today, huge chunks of solid magnetite were in the hoses.

 

[jaydebruyne]

Doesn't matter if the system is drained to test with the magnet works either way

And would stick 5 bar in it and see what it does

I don't have a pump to do that Shaun.. and can't do it with the boiler connected

 

[Last Plumber]

Disconnect the rad valve on each end of the problem rads and check the flow into a bucket or hose.
Make sure you get a good flow from all four ends.
This should help identify any blocked runs etc

 

[jaydebruyne]

Disconnect the rad valve on each end of the problem rads and check the flow into a bucket or hose.
Make sure you get a good flow from all four ends.
This should help identify any blocked runs etc

Sorry, I must be extra thick today! Shut all other rads except problem rads. On 1st prob rad disconnect a valve and attach my flusher to it and see if I get good flow from open end? Doesn't this still have to go round the main circuit?

 

[Last Plumber]

No.
I meant:-

Release the pressure from the system.

Turn both the valves off to one of the problem rads.

Disconnect one valve from one end and turn it to face forward. ( you'll need to plug the rad to stop it dribbling of course, I use a rubber bung).

Then, into a baking tray or bucket or hose connected to the valve you have disconnected, open said valve (carefully) to check that water flows from it.

If it does, re connect it and do the next, just to prove that there is a flow of water from each of those valves.

Once you've done that, you will either see that one or more or indeed none of the pipes are restricted.

 

[jaydebruyne]

No.
I meant:-

Release the pressure from the system.

Turn both the valves off to one of the problem rads.

Disconnect one valve from one end and turn it to face forward. ( you'll need to plug the rad to stop it dribbling of course, I use a rubber bung).

Then, into a baking tray or bucket or hose connected to the valve you have disconnected, open said valve (carefully) to check that water flows from it.

If it does, re connect it and do the next, just to prove that there is a flow of water from each of those valves.

Once you've done that, you will either see that one or more or indeed none of the pipes are restricted.

Oh lol I see what you mean..

just sat in my van eating my sarni.. thinking about it, wouldn't I just need to find the last rad on the circuit, check those valves and if ok I then need to check the main circuit pipework?

Those problem rads aren't the last rads on circuit so wether they're on or off or valves are stuck I should still get flow around main circuit, unless of course the tee of the branch to problem rads is blocked????

Sorry just thinking aloud.. so by checking each valve of problem rads I can potentially find a rough position of blockage of one of the valves or branches to it has not much water??