Finding a blockage in heating pipework

[jaydebruyne]

I did a powerflush a few weeks back and when I was dumping the water the flow dropped immediately. So I rang tech support (Anton) for my pump and he said it's because there's a blockage in the pipework - I tested the pump itself which was fine.

It's a flat with ground and first floor. All rads get hot upstairs but not down. Pipework from the boiler run straight to ceiling/1st floor void and tees somewhere to feed the ground floor.

Based on upstairs rads getting hot I know the blockage isn't there.

So.. how do I go about pinpointing the blockage? I'm thinking taking up some flooring and running across the pipework with a FLIR .. any other suggestions?

 

[ShaunCorbs]

If you can follow/touch the Pipework go around with a magnet

Or if you have flir walk the route should see roughly where the blockage is

 

[jaydebruyne]

If you can follow/touch the Pipework go around with a magnet

Or if you have flir walk the route should see roughly where the blockage is

It's a partial blockage.. sorry shoulda said that.. so the magnet will obv stick to the magnetite?

 

[ShaunCorbs]

Yep which most of the case are what the blockages made out of

 

[jaydebruyne]

Yep which most of the case are what the blockages made out of

Ok cool.. cheers Shaun

 

[Harvest Fields]

Especially if you've drained the water out of the a F&E using a drain cock and not sucked it up with a wet vac

 

[Old Account]

Is that vented or sealed system?
Quite often it's the T junctions or somewhere close to the boiler.
I had it few times though.

 

[jaydebruyne]

Is that vented or sealed system?
Quite often it's the T junctions or somewhere close to the boiler.
I had it few times though.

It's a sealed system.. yeah I'm there week after next to investigate. How did you find the blockage?

 

[jtsplumbing]

Is ground floor 10mm drops ??

 

[Last Plumber]

When the flow dropped during the dump stage, did you try dumping in reverse and if so did it make any difference ?

Where all the rads open at the stage you were at or were you dumping through one rad at a time ?

And as above (jts) are the downstairs individual drops or are the downstairs fed from one drop ?

Are there two heating zones or one ?

Was the water particularly soiled?

 

[jaydebruyne]

When the flow dropped during the dump stage, did you try dumping in reverse and if so did it make any difference ?

Where all the rads open at the stage you were at or were you dumping through one rad at a time ?

And as above (jts) are the downstairs individual drops or are the downstairs fed from one drop ?

Are there two heating zones or one ?

Was the water particularly soiled?

Tried both ways and no difference.
I think all but one we're closed at first then I opened them all - but I can't remember really tbh
Single zone
No idea how many drops as pipework is concealed
Water wasn't that bad no

 

[jaydebruyne]

Is ground floor 10mm drops ??

Not sure as pipework is concealed

 

[Last Plumber]

Zone valves or combi with one open zone from Boiler?

Where were you flushing from, meaning did you remove a pump, connect under the appliance?

Was the flush passing through the Boiler or was it system only ?

 

[jaydebruyne]

Zone valves or combi with one open zone from Boiler?

Where were you flushing from, meaning did you remove a pump, connect under the appliance?

Was the flush passing through the Boiler or was it system only ?

Combi with open zone from boiler
Disconnected system filter on return under boiler and pumped through the valves
Was passing through boiler

 

[Last Plumber]

Anyone open a tap during flush?
Could they have ?
Is it a combi with a diverter ?

 

[Last Plumber]

I'm thinking that if the water was not that bad, it is more likely something changed to restrict flow.
e.g. if diverter moved across it would restrict the path for the water you were shifting around the system. I'm not saying that's the answer but it does sound more like a valve changing than a blockage to me.

It can be a blockage of course and you should not rule that out but i'm trying to help you think outside the box

 

[Chuck]

You may be able to learn something useful by starting with the system 'cold', all upstairs radiators off, circulating pump set low. Then use your thermal imager to figure out the sequence in which the radiators come on when the heating comes on.

The idea is the the blockage will be in the flow or return section immediately downstream from the last radiator to light up. Not a sure-fire solution, of course, but relatively easy and non-destructive.

 

[Vee]

If it once was a open vented system, especially gravity fed hot water, look for blockage where the old cold feed would have joined the system. Generally at ground floor level near where the boiler used to be. Or any position where the cold feed joined the flow. And for the complete joker, if an old anti gravity valve left in the system has finally collapsed, the position of which is your guess on the central heating return back to the old boiler position. Good luck.

 

[jaydebruyne]

I'm thinking that if the water was not that bad, it is more likely something changed to restrict flow.
e.g. if diverter moved across it would restrict the path for the water you were shifting around the system. I'm not saying that's the answer but it does sound more like a valve changing than a blockage to me.

It can be a blockage of course and you should not rule that out but i'm trying to help you think outside the box

UPDATE:
I've just changed the pump as I wanted to rule this out.
The return pipe above the pump going back into the main hex is hot, flow from hex and to system is fine. Flow from system going back into boiler is barely like warm.
Funnily enough the plate hex is also hot whic leads me to think the diverter could be at fault.
When I run the dhw it gets stupidly hot and then cools to probably 40c and stays that way but the flow pipe underneath boiler gets hot also which kind of confirms that it's the diverter and also the plate hex could also have a blockage possible but best to change the diverter first.
What you reckon?

 

[Last Plumber]

UPDATE:
I've just changed the pump as I wanted to rule this out.
The return pipe above the pump going back into the main hex is hot, flow from hex and to system is fine. Flow from system going back into boiler is barely like warm.
Funnily enough the plate hex is also hot whic leads me to think the diverter could be at fault.
When I run the dhw it gets stupidly hot and then cools to probably 40c and stays that way but the flow pipe underneath boiler gets hot also which kind of confirms that it's the diverter and also the plate hex could also have a blockage possible but best to change the diverter first.
What you reckon?

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.

 

[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

----

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

----

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??

 

[Last Plumber]

I'm thinking that if those rads are not working and there is some sort of restriction in the flow around the system, it is a good place to start. As good a place as any.

You will confirm whether there is a clear path to each end of each rad.

It will only tell you if that length of pipe to the rad is clear of course. Beyond that is more difficult, it can flow from either side of a tee, for example.

You may be better releasing the pressure from the rad in your case, that way there will still be pressure in the system to allow water to be pushed from the end you have disconnected. You will have to keep it topped up too.

Once you've done that and ruled out a blockage in each section, you can move on with your thinking.

A lot depends on route too and like I said earlier, we haven't seen the job.

If for example, the two downstairs rads are fed together then a blockage in either flow or return would stop them both from working but if they are both tee'd off separately, you are less likely to learn anything because water can flow form either direction.

I am just trying to think of a good place to start !
Hope this is helping and not confusing the issue.

 

[Last Plumber]

Just to refer back to CHUCK's comments earlier.

This blockage ( if it is a blockage ), could just be partial and could cause the Boiler to short cycle.
That would prevent the downstairs from getting hot.
If that's the case, the you would possibly still get a flow from each leg.

What size are the pipes in the downstairs circuit, are they the same as the rest of the circuit or smaller?

 

[jaydebruyne]

I'm thinking that if those rads are not working and there is some sort of restriction in the flow around the system, it is a good place to start. As good a place as any.

You will confirm whether there is a clear path to each end of each rad.

It will only tell you if that length of pipe to the rad is clear of course. Beyond that is more difficult, it can flow from either side of a tee, for example.

You may be better releasing the pressure from the rad in your case, that way there will still be pressure in the system to allow water to be pushed from the end you have disconnected. You will have to keep it topped up too.

Once you've done that and ruled out a blockage in each section, you can move on with your thinking.

A lot depends on route too and like I said earlier, we haven't seen the job.

If for example, the two downstairs rads are fed together then a blockage in either flow or return would stop them both from working but if they are both tee'd off separately, you are less likely to learn anything because water can flow form either direction.

I am just trying to think of a good place to start !
Hope this is helping and not confusing the issue.

No I hear what your saying, and I really appreciate your help.
NEW: if I turn off the very first rad from the boiler

Just to refer back to CHUCK's comments earlier.

This blockage ( if it is a blockage ), could just be partial and could cause the Boiler to short cycle.
That would prevent the downstairs from getting hot.
If that's the case, the you would possibly still get a flow from each leg.

What size are the pipes in the downstairs circuit, are they the same as the rest of the circuit or smaller?

As far as I can see as I've taken up a couple of boards downstairs is in 15mm. I've strangely got flow now. Gone open one rad at a time and see what gives me the weakest flow and return temp to see if I can narrow it down

 

[jaydebruyne]

I'm just uploading some vids to YouTube to post here so you can see the run of the circuit but here's what I've learned:

Boiler feeds
upstairs small bedroom first = good flow/return
Tees off to
Left to office rad = good flow no return rad gets hot via bypass
Right to hallway rad = good flow/return
Continues right and I pick up a square grid of pipework
Tees left to feed downstairs and to feed
upstairs bedroom rad = good flow no return rad gets hot via bypass
Tees right from square to old gravity pipework and just loops and returns = good flow
Downstairs rads all have good flow and no return all rads get hot via bypass

So basically the return path stops after feeding upstairs small bedroom and upstairs hallway and then disappears.

So I'm thinking to start lifting boards there????

Upstairs circuit

Downstairs circuit

UPDATE:
Found the blockage!! Whoop. It's on a tee after the first 2 rads on the return just before it goes downstairs. Well happy. Thanks so much for all your help everyone, couldn't have done it without you

 

[Chuck]

My reading of the situation is that the return doesn't seem to get back past the 'square grid' but is okay before that. That would point the finger of suspicion at the section of return you are looking at between 15s and 17s in the first video.

If it were my nice wooden floor, I would want to use this a hypothesis and test it by checking that the returns between radiators on the far side of the hypothesised block were all talking to each other but not to anything on the near side of it.

Once you have pinned down the blockage don't let the joy stop you thinking. Whatever you do next needs to get it out of the system not just move it somewhere else. If power flushing failed, as it did in this case, the best strategy might be to replace the blocked length rather than try tricks of the trade to unblock it.

 

[jaydebruyne]

My initial impression is that the return doesn't seem to get back past the 'square grid' but is okay before that. That would point the finger of suspicion at the section of return you are looking at between 15s and 17s in the first video.

If it were my nice wooden floor, I would want to use this guess as a hypothesis and see if it was consistent by checking that the returns between radiators on the far side of it were all talking to each other but not to anything on the near side of the hypothesised block.

Once you have pinned down the blockage don't let the joy stop you thinking. Whatever you do next needs to get it out of the system not just move it somewhere else. If power flushing failed as it did in this case, the best strategy might be to replace the blocked length rather than try to unblock it.

Absolutely! I'm going to cut out the section of blockage and repipe it

 

[jaydebruyne]

The pipework is silver.. what's that about? Def not chrome. I know the pipework is quite old. Just wondering what it's about and if I can solder to it?

 

[ShaunCorbs]

Thin steel (copper shortage in the 70s)

Only compression can't solder

 

[Chuck]

If it looks grey but is fairly soft and silver if you scratch it it's likely to be lead. Lead was still used up until about, say, 1970.

Anyway, the techniques used for jointing lead are not quite the same as for copper tubing and I would recommend you don't make the first time you try it on a customer's system.

There are a couple of people who are active posters (Last Plumber and JustinLead1 come to mind) who have mentioned they have leadwork skills. Probably best to upload a couple of photos and hope they drop in.

 

[jaydebruyne]

Thin steel (copper shortage in the 70s)

Only compression can't solder

Cheers Shaun