8mm microbore rad not getting hot

[Luke Moreland]

Hello,

I have 8mm microbore to all rads (please keep reading), 4 rads up, 4 rads down.

I been living here 6 months and have always had a problem with a rad downstairs, it doesn't turn on. The previous owners had a cabinet there so may well have had the radiator permanently off.

I've done some cowboy work:

• Balanced rads
  
• Turned all rads off but the problem one, inlet valve gets warm (not hot)
  
• Drained system & replaced rad (type11) with new one (type22) of same size and valves
  
• Refilled system and bled boiler and rads
  

New radiator has same behaviour as old.

Other notes:

• When refilling the heating system the new rad had a lovely jet of water from the bleed valve, suggesting the inlet valve allows a good amount of water in?
  

I'm thinking a blockage in return pipes from the rad? Is there anything else I can look at to help diagnose?
Should I consider running some cleaner through the system, is that wise with microbore? I don't want to dislodge some radiator sludge and cause a blockage elsewhere.

Any help is greatly appreciated.

Thanks,

Luke the Cowboy Plumber

 

[Andy™]

probably a blocked pipe somewhere. not always in the return pipe, could be in either

 

[Luke Moreland]

Cheers Andy,

Other than getting at the piping under the floorboards, any other sensible options to try?

Cheers

 

[Doc Hudson]

Welcome to the forum Luke.  When you had the radiator off did you try opening each valve, (obviously into some suitable receptacle) to check how fast the water flowed, (or didn't flow)? If one pipe appears blocked you could drain system then pump air pressure back up the blocked pipe to see if it clears? e.g. With a suitable adapter from 15mm to the rad valve connector you can connect on one of these, https://www.screwfix.com/p/monument-dry-pressure-test-kit/72940  then a push-bike track pump can increase the air pressure to see if it can shift the obstruction. But if releasing the air pressure back out, beware of a jet of black sludge spraying out. So wrap old towel around valve outlet when removing. I used a similar technique years ago to clear a blocked towel radiator pipe. once you have a flow again, get a high does of sludge remover circulating in the system, https://www.screwfix.com/p/sentinel-x400-system-restorer-1ltr/89458 for a period, before flushing again and refill as normal with inhibitor fluid.

Doc H.

 

[Luke Moreland]

Hello Doc,

Thanks! and thank you for the response.

I didn't try either valve when off as I had the system drained, ill do this test tomorrow and see if either flows differently. If it does I'll try the method you suggest.

Will update tomorrow.

Thanks,

Luke

 

[Rob_the_rich]

Good advice from the Doc as usual. Only thing I can add is to isolate the boiler first by turning off the flow and return valves, also isolate every working radiator, and turn off the other valve to the dodgy rad and keep the drain point open with hose attached. So the blockage has somewhere to go.

From the boiler there are usually 22mm flow and return pipes, these sometimes go to a manifold (spider) under the floorboards somewhere. The legs of the spider go to each rad. I have seen blockages at the last leg.

Could also be a crushed pipe somewhere.

Good luck.

 

[Luke Moreland]

Morning,

So here's the latest:

• I've turned both valves off, drained and removed the new rad
  
• Turned them on in turn
  
• Inlet pipe (left hand) to rad is at a trickle of black water (I assumed inlet as it was the only one to get warm previously), right hand has a lovely stream of clean water
  
• Having seen other people have luck pushing air into the system from the faulty pipe, I took my bicycle pump and shot air into it (3-4bar for half a second), expecting a lovely stream of black water, I got nothing, the trickle paused for a good few seconds, then resumed a trickle of black water. It was as if the air pressure failed to pass through the blockage as when I removed the pump the pressure released immediately.
  

Given this, should I proceed to drain the system and give it a go empty?

Thanks for the response rob, this morning I went looking for a way to turn off the flow and return 22mm, from the top of my boiler they go straight into the ceiling with no stop cock/ball lever in sight... I'm at a bit of a loss there.

 

[Rob_the_rich]

Sounds like you have a regular boiler with cylinder and not a combi. Good, combis don't like sludge. Yes, drain the system, but shut off both valves of each working rad first. As above.

 

[Luke Moreland]

Thanks Rob, will do.

How much pressure should I apply to this pipe? 

Will start draining!

Luke

 

[Rob_the_rich]

If air doesn't work, try connecting another hose and try mains water. But not too much, you could overflow the header tank, just short bursts. Remember to add inhibitor if it works. I usually take the air vent off the top of a towel rail and pour it in.

 

[Luke Moreland]

Currently draining,

Will try air first, failing that I'll see if I can craft together a mains hose (have to try convince the other half to go into the attic to monitor the header tank).

If I can unblock this, I'm going to add some X400 and leave it for a couple of weeks, then drain and add inhibitor.

Any reason not to add the inhibitor/cleaner directly to header tank?

Will keep this updated.

Thanks

 

[Rob_the_rich]

If you put it in header tank, you have to be sure all, or most, of it goes into the system. Fine if it is all drained down first, but if the system is already full, it won't get down in there and mix.

Fingers crossed

 

[Luke Moreland]

So I've tapped off all the working radiators and drained the system.

Tried the pump, it pushed some more water out of the drain but no real effect on the blockage.

I sent mains pressure water down that pipe, I got nothing, no water drain, no filling of the header tank, it just seemed to fill the pipe and not move.

Is there a valve somewhere I'm not opening to release the pressure?

Luke

 

[Luke Moreland]

I've decided to refill the system to see what effect the above had.

Leaving the drainage pipe open, I released the ball-cock and let it start filling, as I did yesterday.

Nothing is draining, 15 minutes later, no drainage water and header tank has stopped filling as it is full.

Do I now have a second blockage?  :slap

Luke

 

[Rob_the_rich]

Maybe. Is the header tank dirty? Draining it might have dislodged something into the filler pipe. Or could be an air lock.You could try turning on the heating, but first shut the gas off at the meter, so that the pump runs.

 

[Luke Moreland]

Maybe. Is the header tank dirty? Draining it might have dislodged something into the filler pipe. Or could be an air lock.You could try turning on the heating, but first shut the gas off at the meter, so that the pump runs.

I'll give that a go.

What's the reason for shutting the gas off? Wont the pump still run with it on?

Thanks

 

[Rob_the_rich]

You don't want the boiler to overheat.

 

[Sharpend]

Could I suggest that you attach mains pressure to the microbore pipe to push it back through the manifold into the larger pipe where the fernox may dissolve it. 

 

[Luke Moreland]

I'll give that a go.

What's the reason for shutting the gas off? Wont the pump still run with it on?

Thanks

Pump now on max speed, header tank took a bit more water then slowed to a trickle, no drainage water.

Luke

 

[Rob_the_rich]

If you have a sink plunger, try plunging the header tank outlet pipe from inside the tank.

Also, it could be your drain hose blocked. Shut off drain valve, take it off and see if water comes out the drain point.

Also, open up all your other rads.