Poor Heat Output on Downstairs Radiators

[GoodDIYjob]

Things I’m thinking it might be

1. Historic magnetite blockage at a tee or elbow? How could I find it? Is it likely?

(Originally it would have been a vented system with a hot water tank in the airing cupboard but it is pressurised combi now.)

2. One pipe system? Or two pipe upstairs, single pipe downstairs. Did they do that?

3. Bad tee off upstairs two pipe or did they tend to properly extend upstairs flow and return from last radiator to downstairs?

My current plan

A. Replace one upstairs radiator in the bedroom and the dining room radiator downstairs. Primarily, because those two radiators have broken off bleed valves that can’t be used to bleed.

B. After replacing, I will have been able to see the rad connection to pipework upstairs. Downstairs, I won’t be able to because of the laminate floor which would be a big job to remove together with floor boards running at 90degrees to rads.

C. Once I have the two new radiators, and I have seen if upstairs is one or two pipe, I thought I would put in a system cleaner for a couple of weeks and then drain and refill to see if any improvement. I can’t do that presently as 2 out of 7 rads have broken bleed valves.

Anyone with any advice on either i) if my thoughts about causes are likely or ii) other suggested actions gratefully received.

Thanks

****

Background

2 Storey 1930s Semi, brick cavity walls

32kwh output Combi Boiler

7 rads including small towel radiator, probably about 7.5kwh in total. All rads single panel, single convector.

Only one Thermostatic valve in place in system (others all lockshield). Strangely the TRV is in the bathroom which is set to max and I will probably remove but the towel rail gets hot ok.

The boiler only modulates down to 12.7kwh so you tend to get short bursts of boiler burner firing and quite a bit cycling with Honey CM 927 algorithms as it approaches set points.

Rads except for one of the two largest ones (1800x600) in the front lounge look 30 plus years. The one in the front lounge has been replaced, probably in an attempt to improve performance.

Problem

The issue, is the two big radiators in the ground floor lounge and dining room (both about 1800x600), do not get terribly hot. One has been replaced (mentioned before) the other looks original, as are all the other radiators in the house.

The replaced one has probably the worst performance of all radiators.

It only gets hot at the top and a little on the bottom. The middle section is luke warm.

Things I’ve done

Tried balancing – slight improvement

Tried closing all upstairs Rads – definite improvement, two large rads downstairs pretty hot.

I have also removed the large replaced radiator in the front lounge thinking it was full of gunk. Emptied it outside and cleaned out with a hose but it was very clean. System has inhibitor and a magnetic cleaner installed since we lived here but before us, I suspect it was not well kept.

I can’t get good performance on that front lounge radiator even with upstairs lockshields open a little.

So it has been like this ever since moving in 4+ years ago, it does heat downstairs as is and is OKish in all but the coldest of temperatures. But it does take an age to get the house up to temp esp when cold.

 

[JohnD]

it may well be a balancing problem. If the cold radiators warm up when you turn off the hot ones, you haven't got a blockage.

Circulating X400 for a few weeks is likely to loosen the sediment. A lot of it will be collected in your system filter, so keep emptying it. You can scrape it into a glass jar and have the pleasure of seeing how much you get. You don't have to wait until you have finished your other work before you add it, although you ought to drain after 4 weeks as it starts to lose its power and the sediment will start to settle again. The cost is trifling (about £15)

If you're doing some plumbing, it's a good time to remove old radiators and hose them through in the garden. Also fit TRVs in all rooms except the one with the room thermostat (which should be your main living room)

Buy a small powerful (Neodymium) magnet and hold it against any copper Tees where you suspect sediment. It will be attracted to the black iron oxide. Sometimes the oxide (which is soft) mixes with limescale in hard water and forms a hard blockage that needs to be cut out.

 

[D_Hailsham]

Tried balancing – slight improvement

Tried closing all upstairs Rads – definite improvement, two large rads downstairs pretty hot.

I can’t get good performance on that front lounge radiator even with upstairs lockshields open a little.

If the downstairs rads work OK when upstairs are closed, it's definitely a balancing problem.

How far open is "a little"?

 

[GoodDIYjob]

If the downstairs rads work OK when upstairs are closed, it's definitely a balancing problem.

How far open is "a little"?

Ok, there are 3 rads and a towel rail upstairs.
Rad 1] - 3/4 turn open.
Rad 2] 1 and 3/4 turns open*
Rad 3] 1 and 1/4 turns open.
Towel rail has TRV and wheeled valve. Wheeled valve was 2 and 1/2 turns open. #

* but the other side wheeled valve on this rad was pretty seized and partly closed and I did not want to move it. And I needed the locksheild open that far to get any heat. I now seem to have freed the wheeled valve so it turns, so hopefully is operating now. Not much resistance but it does reach stops.

# can't remember why it was that far open. Maybe a lot of flow is going though there?

 

[aptsys]

Start with just 1/4 turn on the upstairs radiators, maybe 1/2 on the one furthest away.

Is there a gate valve near the boiler acting as a bypass valve?

 

[GoodDIYjob]

Start with just 1/4 turn on the upstairs radiators, maybe 1/2 on the one furthest away.

Is there a gate valve near the boiler acting as a bypass valve?

Will do. Thanks. Think I have been here before but best to try again afresh. There are no bypasses that are visible, unless hidden under the floor.

 

[D_Hailsham]

Start with just 1/4 turn on the upstairs radiators, maybe 1/2 on the one furthest away.

I would try 1/4 turn open for all rads then adjust as required (1/12 turn or less each time).

 

[GoodDIYjob]

So now with
Upstairs:
Rad 1] - 1/4 turn open.
Rad 2] 1/4 turn open
Rad 3] 1/4 turn open.
Towel rail 1/2 turn open. (Wasn't getting very hot with 1/4 turn.)
Downstairs
Rad 4] - 1/4 turn open
Rad 5]Large Lounge Rad] - 1/4 turn open
Rad 6]Large Dining Room Rad] - fully open

The performance of the most problematic radiator Rad 5] is better. It is hotter at top but warm to hot all the way along length and almost to the bottom, once the boiler has been operating for a while.

The other large radiator Rad 6] now feels the worst performing hot at top all the way along but luke warm toward mid section and bottom.

The rads up stairs are maybe slightly cooler than before but still hot for bedrooms. You can hear the water hiss more into the radiators with the lockshields turned down that far 1/4 turn. Much more noticeable than before, presumably from the restriction.

 

[JohnD]

when you have fitted your TRVs, the radiators in the fastest-heating rooms will start turning off, and this is likely to send more heat to rad 6.

Cleaning out sludge may also help.

If you look under the floor, you may find the pipes to rad 6 are shoddy layout (for example it is using the pipes run for rad 5)

 

[GoodDIYjob]

Thanks for the pointers and advice.

Are systems normally that fussy to balance just to get 2x largish (1800x600) but single panel rads to produce consistent heat? That's why I still suspect one of the other problems mentioned, poor pipework, partial blockage, single pipe? Thinking of an extension downstairs next year and a bit nervous now how well the system will cope with another 2.5-3kwh more heat draw without ripping out pipework that is in place to find a problem...

I already have some fernox f3, are better results usually achieved with Sentinel X400, or is it much of a muchness?

I was only going to put new TRVs on the new rads.

But now, having gone round all the valves on the other rads they really could all do with replacing. However, it seems the length of the new valves to the end of the threaded insert are now a bit longer than they used to be. Is seems to be about 52mm from the centre of the valve to where I think the thread would end in the radiator. Most of the TRVs I look at, Drayton TRV4, Honeywell VT200 seeem to be about 60mm now. The tail piece looks longer in pictures on new valves bu maybe misleading.

Are the inserts different now to what they used to be? Or can I leave the original in place so that the pipework doensn't need to be modified on every valve on every radiator? Otherwise it would be as well to bite the bullet and replace the rads as well if having to adapt all the pipework!

Photo included of rad with current valve.

 

[FiremanT]

TBH, you can faff around for an age, but if the system is full of sludge, you will never get to a satisfactory situation. Stop messing around, get some cleaner in, clear the gunk, and then start again

 

[GoodDIYjob]

Too right. But I can't drain and refill the system without replacing the two rads first because of the broken off bleed valves.

Hence the question about fitting new TRVs and Lockshields to the remaining old radiators and the comparability of new valves with the old tails already installed in the rads..

 

[FiremanT]

Presumably, the nipples are tapped directly into the rad, or are they on the end (via a 1/2" plug)?

 

[GoodDIYjob]

Yes, no 1/2 plug insert for the bleed valves. Tapped hole on back of radiators. Can't get to without removing rad and given age, I thought I'd replace those two rads.

Re: fitting TRVs and new locksheilds to the remaing old rads:

I think the issue is they use 1/2" to 3/4" tail insert in the rad. And the overall visible distance from centre of valve to end of thread of the tail I'm looking at could be up to 10mm too long each side of rad. More than pipework will likely move and if I bend the copper it will no longer be true for valve line up....

This must come up a bit?

Is there a different shorter rad tail I can use for fitting new TRV valves (rather than what is supplied) or can I cut the olive end of the tail by 10mm. Pictures of valves with tails on seem to indicate there maybe some scope to shorten slightly....

 

[GoodDIYjob]

OK, so I replaced the 2 old rads with broken bleed screws.

I also took all the remaining rads off wall and hosed outside. There was some black water, more in downstairs rads, but not sure enough on its own to cause circ issues but maybe historic issue before the system was converted to sealed combi with judging by age of boiler is probably 13 years ago.

I put in Fernox cleaner for 1 week after the work and there was a bit of debris in the magnetic cleaner upstairs where the boiler is in the airing cupboard, but not huge amounts.

I put TRVs on all the upstairs rads as a part of the new work. New standard valves and lockshields on downstairs rads.

All the upstairs rads are on about 1/4 turn except towel rail on about 1/2 turn (all as before, when I recently balanced per this thread)


Downstairs:

Rad 4] - 5/8 turn open
Rad 5]Large Lounge Rad] - 1/2 turn open
Rad 6]Large Dining Room Rad] - fully open

There is an improvement when the TRVs start to close down upstairs, as a consequence the downstairs rads are hotter when that happens. Otherwise it is all much the same as it was before and it is hard to get good heat out of both Rad 5 and 6 simultaneously.

There is also a rad 7 in the conservatory which I didn't mention before. It has a TRV set to frost and lockshield closed to about 1/4 turn just to allow some small residual warmth.

Is there anything else I can do>? Would sentinel x800 make much difference? Powerflush worthwhile? There wouldn't be much point doing rads as they've been hosed through....

I'm now thinking the only options left are a restricting blockage on the downstairs flow or return pipework or a some sort of issue with pipework downstairs like single pipe or all rads running off the same 15mm drop feeds or some other fudge. To confirm, would involve lifting a lot of laminate floor and then boards to confirm these aspects and I think I would leave such invasive work until we do some building work, if I have exhausted all else.

Thanks for any other advice.