It's that time of year when one's thoughts turn to the smoothe running of ones
CH system (sad isn't it!)
Before I go into all the details I'd just like to get some expert opinion on the
suitability of the the UPS 15-50 in my system.
The pump has been running for years on the medium setting, but I've always been
concious that the system didn't seem to be running right.
The radiators were not piping hot to the touch, the house didn't feel warm all
over, and the boiler does a lot of 1-2 minute cycling.
Turning to this group again over the last week or so for some tips, I've treated
myself to an IR themometer to do some proper investigation.
As I say at the moment I won't go into all the figures, but the info seemed to
sugest that the pump needed to be on maximum. I've been running it like that for
a few days and things do seem to have improved regards balance of heat even
running all the LSV's open until I'm sure what the state of play is.
My main concernes at the moment are I never see anywhere near 80 degrees C at
the input to the radiators, the boilier is cutting out when the ouput has
reached this temp. The max input to closesest rad to pump is around 70 and the
lowest is around 65. And the Boiler is still short cycling.
So before I try and rectify anything balancing like crazy I want to know if the
UPS 15-50 is powerful enough or not.
I don't know this pump, what head rating is it?
I had similar situation for many years inc boiler kettling at times.
When I changed the pump for the second time I went for a beefer pump with a
It runs a lot quieter on its medium setting and the system works much better
The 15-50 is rated at 5m head.
The annoying thing is I'm sure I fitted this myself soon after moving to the
house because the existing (non Grundfos) pump was very noisy. I no longer have
it to check what the rating was, but I'll pop round a neighbours and see what
Is a 15-60 going to be sufficient of an improvement?
I did flush out and Fernox the system a couple of years ago, but I don't know
how good a job that would have been rated as.
If this is microbore then a more powerful pumps appears the answer. Unless
there is sludge in the system blocking pipes. Did it ever work properly?
The boiler appears to be getting up to temp, so that appears to be working
Microbore requires generally a larger pump than a 15-50. A 15-50 generally
was not used on a house that large. Go for the next size up. and then do
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This means hat either the boiler thermostat has a problem or that the
heat is not being delivered from it rapidly enough. The latter can
be because of poor circulation or because the boiler is oversized/burn
rate set too high for the installation or both.
This does all point to poor circulation as at least one of the
Is the system using microbore pipe (e.g. 8mm)? This may present a
higher system resistance and require a higher pump head.
Have you checked for sludging?
If you have TRVs especially, a better pump option could well be the
Grundfos Alpha. There is a 15-60 model of this which has a 6m max
head as opposed to the 5m of the UPS 15-50. It also adapts its
output to match the resistance requirements.
However, before doing a pump swap, I would check for why the
circulation is poor.
The Boiler is a GlowWorm FuelSaver 55F with a rated output between 35k & 55k
Btu/h. Its anyones guess as to what it has been set to. The manual talks about
putting a suppied self adhesive label by the data plate to record setting but
guess what I can't see one :-)
Yes it is 8mm Microbore (I put it in the Subject line but should have also
included it in the body text too for clarity sorry)
What is the best way of doing this (i.e. least messy )
It doesn't matter greatly - this is a 10-16kW range and I would be
surprised if it is oversized for a house of this size. If you had
said twice this figure then I would have suggested looking further.
Sorry, I missed it in the subject line.
Before doing this, another thing to check is the motorised valve(s).
It could be that this is stuck or blocked. Try taking off the head
and turning the cam manually. You can also try operating the manual
lever on the valve. Sometimes the gearing mechanism in the head fails.
Any problems in this area and the general flow to the CH can be poor.
The fix is to replace the valve, which is an easy enough job..
Next, I would go round and open all of the lockshield valves fully and
check behaviour again. It could be that this is problem. If it
isn't, and there is a sludge problem then you will need to open them
To check for sludging and to resolve:
Pick a radiator where it is easy to get some old towels underneath
plus some polythene. A downstairs relatively smaller one is probably
better since fine sludge particles are likely to have collected more
so in lower radiators. You then need some containers to go underneath
each end of the radiator. I bought cat litter trays from the
supermarket. They're cheap, the right height and will take a fair
amount of water. You do need to take some care because sludgy water
is an effective dye.
With the heating off, turn off both valves on said radiator and
carefully undo one of the union nuts to let the water drain into one
tray, then undo the other. If you do it slowly, you can control the
flow easily. Undo the vent as well.
Once the water has stopped trickling out, lift and tip it to one end
and see if sludge comes out. If there is a fair amount, then you
will have pretty dirty water and sludge before this anyway.
Fasten small plastic bags over the radiator tails and take the
radiator outside. Give it a flush through with a mains hose or
pressure washer. With the radiator still off the wall, carefully
open each radiator valve and check that you are getting a respectable
flow of water. There may well be further sludge in the pipes if
there are long horizontal runs, but there should be enough head of
water from the feed tank in the roof (this is open vented system,
yes?) to flush out the pipes.
It will be reasonably clear if sludge has been the problem by this
time. If it is, then you need to repeat the exercise at each
radiator. Finally, give the system a good flush through with clean
water from the roof tank.
By this time, either because you opened the lockshields, resolved a
problem with the motorised valve(s) or with sludge, you should be able
to get reasonable flow on the pump mid and high settings. Before
my heating refurbishment, I had a 15-50 pump on an 8mm system and it
If you have done the cleaning exercise, I would then put in some
flushing/cleaning agent and run the system hot for a week. Then
drain and flush again.
Once you've done all of this, then an Alpha pump may help further.
If I had still got the old system I would have replaced my pump with
one. As it was, I have one in my new boiler which is controlled by it
to match the heat output. However, I do have an Alpha on my separate
workshop circuit and that works well. The run from the house to the
workshop is quite long and the pipe resistance higher than for a
circuit purely within the house, so the extra head is a help.
However, before splashing out for one of these, I would check for the
more obvious things that are limiting flow first.
OK this might be an interesting one,could be on to something. I've removed the
operating head off the only motorised value in the past now when it has been
making a bit of a noise to find the valve below stuck. With some gentle
persuasion with pliers I've managed to free the valve. How much should this
turn? It only moves probably less than 1/8 of a turn. What is the correct
proceedure for putting the head back on? Does the motor/spring need to be under
tension? Is there a right and wrong way to turn the head when mating up to the
It does not appear possible to just run the CH with the head removed as the
motor continues to turn and the cams cut the pump off on each revolution and
then come back on again, thinking out loud perhaps with the HW switch on it
won't do this.
As it is now the manual overide lever doesn't go under tension in either
Hmm.. That's concerning. It can sometimes happen after the summer
if the heating has not been on. It shouldn't otherwise. You can
avoid the summer issue by turning the heating on briefly evey week or
I haven't looked at one for a few months, but I think it should move a
bit more than that. There are two main designs. One type has a
kind of cylindrical rotating paddle inside and is generally able to
rotate continuously. The other, which seems to be more common, has a
roughly spherical rubber component inside which is mounted
eccentrically. As this rotates it opens and closes against one port
or the other with a 3way valve and just against the port in a two way
valve. These tend to have restricted travel.
There is basically a motor and gear train in the head and a big
spring. With power off the spring moves the actuator position to
one end of its travel. With power on, the motor runs the actuator to
the other end and then stalls (it's designed to do this). Basically
with the power off, you manually move the cam on the valve base so
that it will line up with the head as you locate it into place. It
should only go one way.
It sounds like the spring might have gone or possibly part of the gear
train has stripped because the valve base was stuck.
Normally, with the power off you should be able to slide the lever and
operate the valve, then latch the lever at the far end of the travel
in a notch in the case of the head. If you release it then it should
return under spring tension.
You probably would be able to fool the system by having the valve head
off of the base and creating a hot water demand, as you say, Then
operate the cam on the valve base to the CH position.
If it then works OK, I think that pretty much you will have diagnosed
a faulty head. They are easy to change, but note the wiring
Since you have been having valve sticking problems, I would replace
the valve base as well. You can buy the complete thing pretty
OK I've checked with the neighbour and their's is the Grundfos UPS 15-50 too, so
my memory is obviously playing up and it was in the last house that I must have
changed it! So hopefully it has been properly spec'd for the job.
Also confirmed that their's is set on max speed, and I would imagine they
wouldn't have tinkered with it like me :-)
I've done some more research on the Valve and its a Honeywell V4073A Motorised
Mid-Position Valve. Which according to the spec sheet does only have between
10&15 degrees of spindle movement.
I haven't got my thermometer at the moment, but I could swear since giving the
spindle a good wiggle with pliers the rads "smell" hotter.
Would I be right in thinking that in a correctly spec'd and configured CH
system, the boiler should really be running pretty much continuosly if the room
stat is demanding heat?
Only with a boiler with a modulating burner. A boiler with a fixed output
rate can't possibly be expected to be perfectly matched to the conditions
and outside temperature etc. every day of the heating system. Rather than
modulating down, such a boiler will cycle. However, provided it isn't too
overpowered and the pump is fast enough, the cycling should be reasonably
long in period. Not on for a minute and off for a minute.
Yep, especially with our 9' double radiator. We actually needed 4 people to
move it, and that was with it drained (though sludgy). Even the smaller
1.2m doubles were quite heavy - I'd hate to have tried moving it with water
Cliff, I had exactly the same problems with a 15mm system. The
temperature of the water at the rad inputs is a function of the boiler
thermostat setting as well as the flow rate. I strongly recommend
balancing the system per recent threads here and the faq.
Initially I cranked my pump up to max to achieve the correct drop
across the boiler, but once the system was balanced, reset it to the
mid position. I then replaced it with a 15-60 Alpha + pump simply
because this new unit has an electronically controlled pressure output
to take into account thermostat valve operation around the house.
I was surprised at how much effect on temperature stability and boiler
cycling the balancing had.
I'd second that - use a 6m head Grundfos Alpha. It is rather more expensive
but offers a continuously variable setting to match most applications plus
three fixed settings for special cases. And it's sooooooo quiet.
On Tue, 09 Dec 2003 10:11:27 +0000, Moonshine wrote:
The next size up will fit withoput modification, also the maximum setting
is pretty much the required going rate on microbore systems.
Check that the boiler is delivering at 80+ C. Which is what you should get
when turned on all the way.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
I want to balance my CH system at some time over the next few months. What
is an IR thermometer, where did you get it and how much did it cost? I've
been looking out for balancing thermometers but not found any. I notice
the FAQ on the subject was written by someone who used thermometers he
bought from Maplin.
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