central heating problem

[geoffr]

Heating system is gas boiler (vented system, not combi or condensing) supplying three floors and 24 radiators. Each floor has its own circuit fed of two main flow and return pipes. Problem is top floor radiators do not get hot.

As a test a turned off both the ground and first floor circuits so the boiler was just supplying the top floor and the 2 radiators nearest the main pipes did get hot (too hot to touch) but the remainder just becoming warmer, but not hot. I would have assumed that if the boiler was just supplying the top floor then they should all be very hot.

When all the floors are on the first two floor rads are hot and heat their respective rooms well, but the top floor rads get progressively colder the further along the circuit they are. In fact the end two are cold.

I've been told by the person who had the system installed that the boiler is more than adequate, although the system does date from the early 80s. He also thinks that the pump is working properly as I had assumed that maybe the pump was not working as well as it should.

Has anyone any suggestions as to what I could try. The rads have all been bled and the flow pipe to the first radiator is piping hot (pun intended). As it's a very long run to the top floor could it be a pump issue?

If it is a pump problem would installing a second pump on the top floor work, as the flow pipe at the top floor is piping hot and an additional pump could be used to just pump the hot water around the top floor circuit. Not sure how feasible this is.

[EricP]

You may simply need to balence the circuits by reducing the flow through the rads nearest to the boiler and therefore providing the easiest least-resistance path home for the water.

[EricP]

Sorry. Crap.

"Providing" should have been "reducing"

[geoffr]

Thanks for the reply. I have tried rough balancing but it didnt make a great deal of difference. Also, by turning off the other two floors and diverting all the flow to the top floor I would have thought this would have worked irrespective of how the radiators were balanced.

[Cicero]

=============================== Is there a speed control on the side of the pump? If so, have you got it at its highest setting? - usually 3 speeds.

Check the data disk on the pump to see what 'head' it provides - it may not be sufficient for the height of your house.

Cic.

[EricP]

Yes it should have done something up top, and if it was a sludge problem it would be reasonable to think this would have blocked up the ground rads.

It's not something stupid like someone turning off a balencing tap somewhere by mistake is it?

Hang on a bit, there is far better than me in here. One will be along in bit.

[Nicko]

you should log into easymaintain.com ! They have an ask a question page there and there are loads of useful pages

[EricP]

Fuck off and commit Insecticide, there's a good lad.

[Aidan]

It could be a balancing (or lack of) problem. The entire flow could be short-circuiting through the two nearset radiators, by-passing all the others on the top floor.

Balancing

It may be an air problem, or the pipework may be undersized for the flow rate. You'd need to check through the system from first- principles.

The circulator head has NOTHING to do with the height of the house on a heating system. The rising flow is balanced by the descending return. The system design head is the head of water/ pressure lost due to friction at the design flow rate through the index/least-favoured circuit, i.e., the furthest rad on the top floor.

There's some isolating valves witha built-in flow meter. You could install some of these on the returns from each floor. The name escapes me, Alco-/ Alto- summat. I'll report back when the memory kicks in. This would allow you to measure the flow rate to each floor, a first step to getting it balanced.

No, it generally makes things worse unless it's done properly; a UK plumber/heating "engineer" would be clueless. It's much better to have one pump, correctly sized. I've done it sucessfully with 3" pumps; replacing the main 6" jobs would have been expensive. I'd replace a domestic pump, rather than install additional pumps.

[Aidan]

Taconova Setter.

I was thinking of Altecnic and it's not that at all.

[Ed Sirett]

I think we too have some resources which can be of use. Why are you posting here if easymaintain.com is so useful?

[Ed Sirett]

The last sentence is not true.

The bigger pumps are used where there is more water to move i.e. when there are more and larger radiators. Generally the 5m pumps are good for up to 24kW and the 6m ones somewhat above that.

The height is not relevant as the pump only has to circulate the water, the return pipes balance the pressure on each side of pump no matter how high the house is.

[Dave Plowman (News)]

Are the flow and return pipes to the top floor both scalding hot in this condition? And can you check them at the furthest point from the boiler? My guess is you have an airlock somewhere - despite there being water in the rads.

Remember a pump doesn't actually have to 'lift' water - merely circulate it against the resistance of the pipework. So if it's heating the first rads on that floor with all others turned off it's unlikely to be a pump problem. What happens if you also turn off the first couple of rads on that floor that do work?

[geoffr]

The flow pipe is scolding hot, but the return pipe is luke warm. Also, when I turned off all the radiators on all floors expect the furthest one from the boiler on the top floor the radiator did become hot and the return pipe was warmer, but still not hot.

If there is an air lock I would be grateful for any tips about how to remove them. Is there any point in disconnecting a radiator, emptying it and then re-conencting it?!

The other radiators then all warm up relative to what they were. If I just leave the last two on they both become scalding hot, although the lower part of the last radiator is only hot.

Is it safe to assume that as the flow pipe supplying the top floor and upto the point of the first radiator is scalding hot then its not a pump problem?

Other info which may be of use is as follows:

The main flow and return pipes are 28mm and the circuit pipes on each floor are 22mm with the branches of 15mm.

The guy who had the system installed has drawn a rough plan of the circuit and the two coldest radiators are on long branches of the main circuit and the furthest must be about 20 feet away from the circuit.

The pump has five settings and it is set to 5

Thanks for all the replies.

[Ed Sirett]

No.

What make and model? Is this something like and Alpha with various modes?

Is there a bypass circuit and what is the setting of the valve?

The first job is to make sure that you can get each radiator to work by turning all the others off.

The next job will be to turn on all the rads and then start by turning down all the ones that get hot so that the non adjustable valve (the lock sheild) is only open "a bit". Eventually you should be able to get them all hot.

[geoffr]

Its a SMC Commodore 130 and it rated at 73w to 130W with a maximum working pressure of 6 Bar.

I dont think so, but I'm strictly a layman so I'm not sure what I would be looking for!

I have managed to get them all hot on an individual basis by just leaving a couple on and turning the rest off.

I have tried this before (balancing?) but I end up with them all being only luke warm at best. I am wondering whether it is a pump problem, as if it was an air lock am I right in thinking that the ones affected would never warm up until the air lock had been removed. Also, if I reduce the flow to the other two floors this does make a difference to the top floor rads.

Thanks again for your help

-

[Ed Sirett]

OK. I'm not familiar with that model,let's assume it has 5 speeds and is set to max and is working OK.

At this point the best advice is to get some pro help. The bypass is pipework that allows the primary water to flow even when all the radiators are shut. In more modern installations it may be inside the boiler itself and is pressure sensitive so it does not affect the heating performance during normal operation.

OK. So no air locks, and no 100% blockages.

yes that's what the game is called.

but I end up with them all

OK either the pump is not doing it stuff well enough or the boiler is grossly under powered for the house, or there is an open bypass which is killing the system.

I am wondering whether it is a pump

May be.

Get some help as the next step will depend on a judgement about the boiler power and the bypass circuit (if fitted).

You could try a new pump which could at worse be £50 of unnecessary expenditure.

[geoffr]

Thanks again for your reply Ed, but before I get in professional help I've just got one further question.

I have now noticed that when I first turn the heating on the boiler fires up as normal, but while the radiators are warming up the boiler does not run continously. It keeps turning off and then firing up again. I do understand that when the heating is on the boiler is not running continously, but I would have thought that when the radiators are initially warming up the boiler would be heating the water until they are all hot. It seems to turn off more frequently when the majority of the hot water is being directed to the radiators furthest away from the boiler. It also takes what appears to be a relatively long time to heat the radiators furtherest from boiler when only they are on.

I'm am just wondering whether this may indicate a particular fault or whether its perfectly normal!

[Ed Sirett]

It eliminates the possibility that the boiler is grossly under powered and confirms the other possibilities.

[The Natural Philosopher]

That generally indicates that the radiators aren't pulling heat out of the water enough..may be blocked radiators..