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Plumbing - blocked pipe?


oscarsdad
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So in my house we have a lot of radiators....27 I think. Powered by a 2 year old Worcester Bosch biggest size combi boiler controlled by Hive. 
 

The radiator in our bedroom takes the longest to heat up being furthest away and it did have an airlock in it which I cleared following YouTube and some garden hose. 
 

I have noticed this week that the kitchen radiator isn’t getting hot at all, the incoming supply is cold - the pipes are accessible under the stairs and are hot until just after a 90 degree bend from horizontal to vertical, where the go cold. So I’m thinking there is a blockage. 
 

I don’t want a plumber coming during lockdown, I am considering turning all other rads off and then running the heating to see if it clears - any other suggestions from the wise?

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4 minutes ago, TIGHTCHOKE said:

If you are able to pinpoint the possible blockage it may be easier to just cut that piece out and replace a section of (I presume) 15mm copper pipe.

 

You bleed to get trapped air out of one or more radiators but then have to pressurise the system to get it to work.

I was thinking that...the system was repressurised after bleeding and clearing air lock so it isn’t that (it’s really easy on the boiler I have). 
 

I am pretty confident I know where the pipe goes from hot to cold so did wonder whether just to replace that section. I may just live with it until the summer - luckily the kitchen is warmed by hall and dining room and we onl6 noticed as I happened to shut the kitchen doors one night and it was cold in there the following morning. 

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2 things to try. 

1  turn off pump and check system pressure, wait a few minutes and vent rad in question with pump off then top up system pressure .

2 if this did not work go to LSV on rad and close noting how far it moves then open fully and see if rad gets heat.  Once hot close LSV and reopen to previous point.  It is not unknown to get a small bubble causing a lock/blockage in a near closed valve.

 

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4 minutes ago, Yellow Bear said:

2 things to try. 

1  turn off pump and check system pressure, wait a few minutes and vent rad in question with pump off then top up system pressure .

2 if this did not work go to LSV on rad and close noting how far it moves then open fully and see if rad gets heat.  Once hot close LSV and reopen to previous point.  It is not unknown to get a small bubble causing a lock/blockage in a near closed valve.

 

Thanks - will give that a go. 

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2 minutes ago, walshie said:

It's very unlikely that a pipe would get blocked to the extent that hot water couldn't pass through it. I'd be looking at the radiator valve as the culprit. 

That was my first thought, the TRV pin wasn’t stuck but the pipe being cold for several feet before reaching the radiator led me to the blockage conclusion - hopefully it’s a bubble and the suggestion about will clear it. 

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2 minutes ago, oscarsdad said:

That was my first thought, the TRV pin wasn’t stuck but the pipe being cold for several feet before reaching the radiator led me to the blockage conclusion - hopefully it’s a bubble and the suggestion about will clear it. 

If the valve is completely shut, the pipe will be cold for several feet before it. Anyway, hope you get it sorted. 

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Close your other radiators trv valves and run your heating.

Chances are it's a little air lock stopping the flow to that radiator. By giving it the full system flow it should clear.

Then go open all the trv,s if it gets cold again open the lock sheild valve to fully open the five turns and see if this works, if not your system needs re balancing.

Every single system I've worked one over the years has at least one rad that gets all or most of the air and needs bleeding regular, one that's a pain to keep balanced and working.

Sometimes the only way to clear a air lock is the backfill via a hose from the mains. Best left to professional.

Edited by figgy
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like has been said turn off all your rads apart from the one not working to push all the flow to it, help with bleeding make sure the trv and manual valve on it are fully open .if it gets hot move on to next phase.

chances are with 27 rads your system is not balanced and the one not getting warm is the last one on the loop.

water is lazy and will take the easiest path so the rads nearest the boiler need to have the manual  valve on them  cranked right down   just cracked open or all the flow will be lost in the first few rads and returned back .as you get futher away from the boiler open them a bit more until the far one will be fully open.

hope that makes sense

Edited by Remimax
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11 minutes ago, Remimax said:

like has been said turn off all your rads apart from the one not working to push all the flow to it, help with bleeding make sure the trv and manual valve on it are fully open .if it gets hot move on to next phase.

chances are with 27 rads your system is not balanced and the one not getting warm is the last one on the loop.

water is lazy and will take the easiest path so the rads nearest the boiler need to have the manual  valve on them  cranked right down   just cracked open or all the flow will be lost in the first few rads and returned back .as you get futher away from the boiler open them a bit more until the far one will be fully open.

hope that makes sense

It does, thanks - the cold radiator in question is by far the closest to the boiler, that said, I have only been in the house a year this week so with extensions to the house having been made, I do not know the pipe routing but I will be amazed if it is the last one on the system. 

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2 minutes ago, oscarsdad said:

It does, thanks - the cold radiator in question is by far the closest to the boiler, that said, I have only been in the house a year this week so with extensions to the house having been made, I do not know the pipe routing but I will be amazed if it is the last one on the system. 

in that case good chance its been plumbed really badly and airlocked or you have one of the valves siezed shut.

you could always shut both off  drain /disconnect and test each end into a bowl for flow.

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7 hours ago, The Heron said:

Sometimes plumbers will put a valve at the end of the system between the flow and return to help balance the system and as you have such a large system this could be the case 

Pressure differential bypass valve, ideal if you have radiators shutting down, stops a lot of water flow noise going through the rad valves. 

Pressurising a system does not stop airlocks. Just does away with feed and expansion tanks by making it a closed system. If you have a tall house and tank in roof space you can get decent pressure, 1 bar per 10meters of height.

Most air in closed systems are from fresh water being added or from corrosion gasses in radiators.

Edited by figgy
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I have a similar sized system (28 radiators (mostly doubles) and 42KW Worcester standard boiler (not combi)).  My system was 'new' in that the whole house was replumbed about 4 years ago.  A few points/tips;

  1. These are quite large systems and have (in my case anyway) a variety of different radiator sizes (from a very big double to towel rails), and some pipe runs are 'complex' being an old listed building where the pipes have to go round various 'obstacles'.  Balancing the flow is critical to getting it to work evenly.
  2. A large pump will be needed; these (usually) have different speed settings.  You will probably need the maximum speed.  Some pumps also have a 'proportional' pressure control - which I have not had success with.  (My pump is a Grundfos with three constant speeds and 3 proportional speeds).
  3. Balancing a big system is both time consuming and takes some knowledge/practice, and is never perfect - because thermostatic valves (TRVs) alter the flow unevenly as the house warms up.  The 'ideal' is to have a drop between 'flow temperature' and 'return temperature' that is much the same across all of the radiators before the TRVs begin to restrict the flow (at which point the return temperature of that radiator drops as the flow is restricted).  Typically about 25 degrees drop from a flow about 70 C to a return of 45 C when the heat requirement is high.
  4. Radiators usually in a modern system have a TRV at one end and a 'Lockshield valve' (LSV) at the other end.  The lockshield is a sort of 'restrictor' that restricts the flow and are used to 'balance' flow.  They are usually adjusted with a tool and once set, not touched again (other than to remove the radiator for decorating etc.)
  5. Generally - large radiators a long way from the boiler need the LSV fully open ........ and smaller ones near the boiler may only need the LSV to be open half a turn or less.
  6. If radiators (TRV open) have a very slight temperature drop - the flow is too high (water whizzing through before it gives up it's heat) - and if a very big drop - the flow is too low (water getting cold before it gets through the radiator).
  7. It is a tricky procedure because as you shut some down by restricting the LSVs, water is effectively diverted elsewhere .......... and you want to end up with as much flow as possible (i.e. big distant ones fully open).
  8. When LSVs have to be very nearly closed (such as a small rad near the boiler) - they can gradually block due to sediment because the LSV has a very small 'gap'.  Occasional opening to full and closing to the old setting clears this.  Measure how much of a turn to close - wind open fully - and run for a few minutes - then turn back to closed - and open by the original amount measured.
  9. TRVs can 'stick' - usually closed.  Most are freed by either a sharp tap, or removing the head and gently tapping the pin.  There are various Youtube examples for different types.  I have found my modern Danfoss valves rarely stick, but do leave them fully open in the summer months when the heating is not in use.
  10. IF you choose to rebalance a big system from scratch, be aware that it can be quite time consuming to get right as the time to 'stabilise' after adjustments is prolonged.

I hope this helps and good luck!

Edited by JohnfromUK
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6 minutes ago, blackbird said:

That’s what I was thinking 27 radiators

As mentioned above, I have a similar sized system with a Worcester 42 KW conventional (i.e. non combi) boiler.  It was carefully calculated and normally works well within capacity (i.e. burn rate modulates down after the initial heat up) and it easily maintains the right flow and return temperatures (in my case about 65/40 C) works fine and allows the condensing aspect to function well.

In very cold windy weather and with the whole house heated it does have to work hard, but much of the time (especially this year) the main big rooms are turned right down to 'gentle background warmth only) and I live in a subset of smaller rooms.

Basically you can measure each radiator, look up the power (KW) of each at the selected water temperature, and add them all up.  That will tell you if your boiler is adequate.  42 KW is probably 2 to 3 times the power of a 'typical' boiler and should manage 27 rads and most rads are about 1 to 2 KW

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