Posted by: @bobtskutter

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Are the pipes to living room radiator in a concrete floor? Do they have insulation?  You're probably loosing heat into the slab.

You might want to set your pump back to CC3 just to see if makes any difference.

Yes they are in a concrete floor. I think they were covered in Denso tape for corrosion protection, not sure about insulation. It was a long time ago...

I did check the living room rad after opening all the lock shields when I was still on CC3, it was cold then as well.

I do have an infrared camera and thought it might be possible to find out something using it. It confirms the rad itself is as the same temperature as its surroundings, with just a barely detectable bit of warmth in the feed (~20 degrees). The penultimate rad on the way to the living room rad is interesting. You can see it's supply pipes in the floor, coming in from the left, but nothing going out on the right towards the living room: 

This suggests some sort of blockage to me, but of course there is no clue as to where it is. The pin on the TRV (the head is off) moves freely but I wonder if you can get rogue one where the pin moves but the actual shut off bit doesn't. Or whether the same thing can happen with lock shields, appear to be open but the are not.

The radiator circuit had a very thorough power flush at installation time (Feb 2022), partly because even back then the living room rad was cool. 

@judith - yes, Bob's help has been invaluable - thanks Bob!

I installed the pipes myself (1986?) and all I remember is the Kango and the dust! I'm pretty sure I didn't do anything silly but I can't remember about the insulation. I thought I had some photos taken at the time, but if I do have some, I don't know where they are!

See also the above about no heat getting beyond the penultimate rad. If heat was getting lost to the slab, I think I might see some heat past the penultimate rad when then fizzles out.       

Posted by: @cathoderay

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The pin on the TRV (the head is off) moves freely but I wonder if you can get rogue one where the pin moves but the actual shut off bit doesn't

Yes.  If the pin feels sprung then no problem.  If it moves freely then the closing piece (not sure what it's called) may be stuck.  A few sharp taps with a hammer directly opposite the outlet to the rad usually frees it.  Standard procedure at the beginning of the season!

Posted by: @jamespa

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If the pin feels sprung then no problem.

Moves freely but definitely against a spring with increasing resistance as it is pushed down, not flapping in the breeze freely. 

@cathoderay you're very welcome.

If your living room radiator got warm when you had the system balanced with the lock shield valves pinched in then the pipework is probably not blocked, at least not completely.

It's likely the long(ish) run of narrow (15mm) pipe is creating too much flow restriction.  The flow path through a 15mm TRV is a narrow orifice about 4 or 5mm.  If you can change the TRV for a simple lock shield valve it might improve things (but that's not going to be an easy job).

My in-laws once had their single pipe "solid fuel type" heating system power flushed and TRV's fitted.  Most of the radiators stopped working because of the narrow flow path through the TRV's (single pipe systems have almost driving force to get the water into the radiators, it's all done by convection).  I swapped several TRV's for basic lock shield valves to improve the system.

It's not impossible that a T-piece on the branch to the living room radiator is partially blocked.  That could direct the flow away from the branch to the living room.  You would have to disconnect the living room radiator and vent water from each valve (TRV and lockshield) to clear each branch.  (Had to do that at the in-laws as well).

Bob

Posted by: @bobtskutter

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If your living room radiator got warm when you had the system balanced with the lock shield valves pinched in then the pipework is probably not blocked, at least not completely.

It did get warmer, but never as warm as the other radiators. I agree the evidence points to a partial restriction, significant enough to reduce flow in normal running to the point where effectively no heat arrives at the radiator. It is about 9 metres each way, and as I think I mentioned has more than its fair share of 90 degree elbows where the pipe work travels round from the old radiator wall to the new radiator wall. 

Posted by: @bobtskutter

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The flow path through a 15mm TRV is a narrow orifice about 4 or 5mm.  If you can change the TRV for a simple lock shield valve it might improve things (but that's not going to be an easy job).

That is a very tight orifice! Being so small, it must also be vulnerable to blockage, though I have to say I think my system despite it's age is fairly clean (the water that came out when I bled the rad yesterday was clear). It might be worth cycling the TRV through its full range a few times, and then applying @jamespa's light touch tap with a hammer. Changing the valve will be a big job, full system drain down as the radiator is on the ground floor. 

That said, I have never been happy with the aesthetics of the radiator. It is a large K3 taking up about half of an inside wall, in a room with limited wall space. It dominates that part of the room. It 'had' to go on that wall as the adjacent wall (where the old rad was) was not big enough to take a properly sized K3. The upshot of all this is I have for a while been mulling over finding a large enough vertical 'designer' radiator than can go where the old rad was, but when I have looked, all I have found is ludicrously priced designs that look like they have fallen off a space ship, and still don't have enough output. A low ceiling is another constraint. The room's calculated heat loss is 1700W, and at heat pump temperatures that means a big radiator.

Posted by: @cathoderay

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and then applying @jamespa's light touch tap with a hammer. Changing the valve will be a big job, full system drain down as the radiator is on the ground floor. 

Just to say you do need a firm tap (occasionally several), just opposite the inlet to the radiator.  Hit it about as hard as you dare.  Sometimes this partially frees it and you need to 'work' the pin to free it completely.  Your flow and return are reversed I think which may mean that the water pressure is working against you.

Posted by: @cathoderay

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It is a large K3 taking up about half of an inside wall, in a room with limited wall space.

I potentially had that problem for one of my rads in a living room.  FWIW I ended up with a Mitsubishi fancoil.  Expensive (~550) and you can hear the fan, but its no more disturbing than the fridge which is in the same room and not at all tonal, just white noise.  Looks very smart and neat, (they are Italian and it shows IMHO).  

@jamespa - I'm not convinced the valve is jammed shut (the pin has the expected spring resistance), more that it is blocked, the idea being that rattling it by tapping it might free a blockage if there is one.

I hadn't thought of using a fan coil in the living room, certainly worth looking into. 

@jamespa  please can you share the details of the fan coil you used.

Thanks

Bob

Posted by: @bobtskutter

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@jamespa  please can you share the details of the fan coil you used.

Thanks

Bob

Mitsubishi iLife 2 slim. https://www.saturnsales.co.uk/I-Life2-Slim-DLMV-170-ATS2-Fan-Assisted-Radiator.html

@jamespa - thanks. It looks like the larger version will just fit where the old radiator was, and the max output at heat pump flow temps is 2.11kW, more than enough for the room (1700W). I may need to check the flow rate though! City Plumbing Supplies do the larger one for £505.44 inc VAT and delivery, with the possibility of discounts.

Posted by: @cathoderay

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I may need to check the flow rate though!

Shouldn't be a problem, in common with many fancoils it has a very short pipe with lots of fins on, not a long pipe.  That means it doesn't add much to system volume or resistance.

At full output expect to hear the fan quite distinctly (but not annoyingly, at least not to me).  Mine rarely goes up to full speed. 

One thing to watch is that it shuts down when the FT < 30C.  So far this hasn't been a problem, but at the end of the season it might be as I might end up operating at a FT just a bit under.  This setting isn't adjustable, but Im guessing a resistor in series (or parallel as appropriate) with the sensor might fool it into thinking the FT is just a bit higher than it is.  I might have to make it switchable summer/winter if I use the unit for cooling, which I just may.  That said the room where it is has another radiator and gets lots of solar gain, so it might not matter when we get to that point in the season where Im still heating but at a low FT.

The flow restriction to your living room radiator is likely to be the pipes and valves.  Swapping the radiator for a fan coil might not give you additional heat output because it's not the radiator that's causing the "restriction".  If you're considering swapping the radiator for a fan coil you're probably also considering removing the TRV and installing a full flow valve.  Why not try removing the TRV and installing a full flow valve to see if it makes any difference.  It might save you £500.

Bob