"The important thing is that the return water coming out of each radiator is good and hot. If it's only warm you need to open its Lock Shield Valve (LSV) some more, or if it's already wide open you have to close the LSVs on the hottest radiators instead."
The problem is that the 2nd floor rads are still not hot (just warm), and the ground and 1st floor rads now have cool return pipes. If I open up the LSVs so get hot return pipes on the ground floor, then the
2nd floor rads are even less hot.
Do you think I need a bigger boiler (it's already a pretty big one)? Or would a faster pump help?
The size of the boiler makes no difference to the water circulation. If you aren't getting even temperatures across all the rads, then this is the problem.
Is the boiler running continuously, or is it cycling on and off on its own stat? If the latter, the boiler has spare capacity - you're just not harnessing it fully.
The water needs pumping round with a bit more urge - so that you can get water to the 2nd floor radiators without starving the others. Does your pump have a higher speed setting than you are currently using? If so, turn it up. If not, fit a more powerful one.
You need to be able to get an adequate flow to all radiators - with a uniform temperature drop - with all the TRVs wide open. Only then should you turn down the TRVs to establish the right comfort level in each room.
Oh, so now you think that everyone that owns a central heating system is capable of calculating the required pipe sizes. That's rich coming from the one that refers to all diyers as incompetent.
And do try to remember to snip, there's a good chap.
On Wed, 06 Oct 2004 04:14:24 -0700, Simon Langford wrote:>
There are number of ways forward:
1) If the boiler is fires up and never stops on its own thermostat until it's turned off then it simply is not powerful enough, or there is something very wrong with it. This is possible but less likely than (2).
2) The pump is simply not pushing the water around hard enough. The boiler is working fine, it gets hot and cuts in and out as needed but the water is not moving around well enough for the number of radiators and size of house and size of pipe work in your installation.
3) As (2) but the pump has become very ineffective - I have known pumps to erode away in adverse circumstances.
Details of the make and model of boiler would be useful also is the pump in the boiler or is it elsewhere. If the latter then it may well be a two or 3 speed unit and all you have to do is turn it up a notch.
It seems suspicious that it's just the higher radiators that don't get hot. Have you tried bleeding them to check that they're not full of gas? Your central heating has presumably been idle all summer and gas released by corrosion may have collected upstairs.
I pretty much summed up all that I've done in my first para - i.e. just closed down the LSVs on the hottest (ground floor) rads, hoping that would force some hot water to make its way up to the second floor. I've not done any proper temperature readings (except using my hand!). All of the go/return plumbing is concealed below the flooring, so I cannot tell how the plumbing is routed. There is about a meter of exposed 'main' pipework near the boiler and I guess the external diameter is about 25mm.
I tried that last night - with all the others locked off, my top rads heat up nice and hot. So no blockages, airlocks, etc.
This does seem to be the case.
OK: I have 10 rads on the ground floor (double panels ranging from
50cm to 120cm, and a 200cm single panel), 2 on the first floor and 2 on the second floor. And a chrome towel rail on each floor. The boiler is a Worcester Highflow 400, running off LPG (costs a fortune!). It has an built-in pump which is not speed adjustable. (The manual says "if there is a switch, it will be factory set to maximum and should not be adjusted".)
The whole system was brand new about 18 months ago. I had the same problem all last winter (we had to get electric heaters on the top floor!). Surely whoever installed it would have used an adequate size boiler? It's physically much bigger than in my last house -- and that was a 3-storey house too. I wonder whether the problem is that there are so many more rads on the ground floor than on the upper floors?
To be fair, I think the OP has made some steps in that direction. Where he probably needs help is in judging the amount to open up the LSVs on the lower radiators so as not to starve the upper-floor units of heat. I spent some time re-balancing my system a couple of years ago, and was quite surprised that some radiator valves literally only need to be open half a turn (maybe even less), while others needed to be fully open. I didn't use a thermometer, it has to be said. All my radiators have TRVs and I wasn't entirely convinced that you can follow a rigid approach with one valve when at the other end of the radiator there is another working all by itself (and in general they are almost never fully open or closed but constantly adjusting, especially during times when the water is heating up). Even now, some radiators take a little longer than others to warm up, but once the system is fully heated, they are heating about as evenly as I would want.
With the vast majority of the OP's radiators on the ground floor, these are the ones that will, in the main, need to be virtually closed off. He does have quite a large load but the boiler is spec'd at 24kW and ought to be able to cope. Likewise, one would hope the boiler designers fitted a suitable size pump integral pump.
It's some time since I've read the FAQ, but isn't this covered in that? Gate valves tend to be very non linear, as opposed to 'tap' types.
It makes life so much easier. And accurate DVMs that incorporate a temperature probe are cheap these days - and will find more uses than a pipe thermometer.
I didn't believe just how important taking time to balance the system properly was - thinking you could just rely on the TRVs. But if you want the house to warm up evenly, it's vital.
But you need to key down the flow to the rads that are the offenders before worrying about the pump. I've also got a three story house, and my pump is set on minimum (out of three settings).
Has it always been like this? If not, has anything been changed?
The 'about 25mm' pipe would either be 22mm or 28mm.
What diameter pipes connect to the rads on 2nd floor? If they are skinny (8 or 10mm outside diameter) that is a likely cause, assuming you have properly balanced the system. Even 15mm may be pushing it depending on the length of run and size of the rads.
If that is the problem you just might be able to fix it with a more powerful pump, but I wouldn't hold out much hope because if the pipes are too skinny the resistance goes up *very* rapidly as you try to increase the flow rate. The length limits for the runs are really pretty firm, and if exceeded for a given heat load (i.e. radiator size), there is not much alternative to replacing with a larger bore.
On the other hand it may be the pipes are OK, but you have one of the other problems I mentioned.
That is a good indication (but only that) that it is just a balancing problem. What you need to do now is *very* slightly crack open the LSV on the downstairs rads to see if they can be got hot without short-circuiting the upstairs loop. It is very important not to open the LSV any more than what gives a hot downstairs radiator. Opening it too much will give no additional benefit to that rad but will cause it to bypass water that should be going to the upper floors.
As others have said, you do need to go further than these rough tests and carefully follow the balancing procedure. I have high hopes that that is all that is wrong. A £20 IR thermometer will be a great help to speed up the process which is otherwise very tedious. If you use one, I find a square of black PVC insulating tape stuck to the pipes to be an excellent standard surface from which to measure the temperature.
Not sure what you mean. So far the rads are not balanced to equally heat, so we cannot yet draw conclusions about the boiler.
Don't forget the towel rails are rads that need balancing too. They can also short-circuit the upper loops.
Sounds like a typical installation where it is all carefully designed by a heating engineer, and then installed by a plumber who has no idea of the importance of balancing. In the groups experience, it seems that virtually the only systems that get balanced are those done by DIYers. It's probably not relevant here, but do you have a decent set of controls? i.e. programmer, room stats, separate control over hot water/central heating, and possibly ability to turn off upstairs/downstairs zones?
If you can't get it balanced I should start raising hell with the installer on the basis that it was never working to spec (e.g. to raise rooms by about 24C over outside temp of -3C). This will be aided if you can show charts of room temperature attained vs outside temp. The inside/outside differential is roughly linear, so that if the rad in a room raises it by 5C more than outside on a warm day, that is also what it will do when it is -3C outside. So measure room temps and convert them to what it will be when the outside is -3C and ask the installer what he intends to do about it. These measurements should be with all the room, TRVs and boiler stats turned to max.
Is the boiler producing very hot water at its flow, and with cool returning water? If so the heat must be going somewhere, assuming the pump is running!! Is it running? Can you hear it/feel it vibrating? Even so it may still be damaged if any vanes are broken off inside. Take the end cap off and see if the spindle is spinning - only an egg cup of water will come out.
Try closing off the ground and first floors, open the top floor. Then gradually open the first floor to balance the first and second floors, then crack the ones on the ground floor open a tiny bit at a time to balance them with the first and second.
Bit of an assumption there, if there is air trapped in the top of the system it could make a massive difference when the lower rads are open.
Thanks for all the replies and help everyone. I think I'm getting somewhere now. I screwed down all the radiators and towel rails apart from the top floor and ran the boiler for 30 minutes. Sure enough the top floor gets nice and hot.
Then I opened up the ground and first floors just a little bit, until some warmth came through. This morning when the heating came on, everything was nice and warm.
When I checked the pressure in the system before forcing the heat up to the top floor, it was at 1 bar. After getting the top floor hot it was down to almost zero, so maybe there was a blockage somewhere which has now been shifted. I'm going to do a proper bleed tonight, and might get myself a digital thermometer as recommended here, to do a proper balance.
I'm still pretty sure that the boiler runs flat out (i.e. never cuts out under its own thermostat). It is quite a large house, especially the ground floor which is more than twice the area of the other floors and has some very high ceilings. So maybe a 24KW boiler is only just up to the job? We're about to remove a large radiator from the kitchen and put a wood burning stove in its place, so that might help the boiler load. (I know the kitchen will be colder when the stove's not lit...)
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