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Phil Addison
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Default Another heating problem question!

"Phil Addison" wrote in message
On Thu, 11 Dec 2003 18:37:04 -0000, "David Hearn"

In the case of 3), the by-pass circuit is returning too much hot flow water
back to the return, and the return at the boiler may be almost as hot as the
flow. However, the return water from the radiators, before it joins the
by-pass return, will be too cool.

No 3 might be something - I've covered that below though.

I think not, having read the info below.

What procedure did you use to re-balance? Are you starting with all LSVs wide
open, and turning DOWN the LSVs on the HOT rads according to, rather than just trying to
open up the cool ones?

Well, my procedure was to open up all the lock shields and then turn the
lock shields on the rads closest the boiler (the hottest ones) to get them as
closed as possible yet still giving an adequate temperature drop and still
hot to the touch. It wasn't a 'to the letter' following of the FAQ.

Forget about the radiator body temperature - the key is to get the return pipe
of each radiator equally hot. It's easy to think the rad is hot to the touch
when in fact its only the top or the flow side that is hot. It's only when the
exit (return) pipe is hot, that you can be sure you have a good hot flow
through it.

If you want a 'quick' balance without the effort of the precise procedure, the
method is to locate the coolest and the hottest rad returns by hand, then
gradually close off the LSV on the hottest one. This will make that one
cooler, and divert some of its hot water into the cooler ones, which will
become hotter as a result. You just keep repeating this on various pairs until
all returns are as equal as you can tell.

50C on the flow is not enough. What is the temperature at the boiler flow on
number 5? It should be over 80C. It seems you have hardly any flow to this rad
so you need to fully open its LSV and close down some of the hotter ones.

I've yet to manage to get the thermometer onto the boiler pipes directly
(very tight squeze above the boiler or floorboards up directly above the
boiler). I'll try to get this done tonight and see what's actually coming
out of it.

So long as there is a good flow rate, there will not be any significant
temperature drop along the flow pipework, so you do not need to get right up
to the boiler tapping. In fact the flow connections on each rad should be
within a few degrees of the boiler output temperature.

Is that what you are using to measure the flow and return temperatures? If so,
the results are probably miles out!!

No, I've got 2 pipe thermometers for the radiator feeds - I'm just using
that thermometer as a basic indication of room temp.

Some folk swear by them but I could not get consistent readings from them, and
they take ages to stabilise. I got good results with a Maplin thermocouple
meter, but have just ordered an infra-red thermometer from CPC for 35
delivered (thanks for the tip, Moonshine, in thread "Is Grundfos ups 15-50 man
enough for 15 year old 4 bed detached 8mm Microbore CH system")

It seems to me that (1) in changing the boiler stat you have now got the
boiler set at too low a temperature. It should be set at up to 82C flow

I'll check that tonight hopefully.

and (2) you must have closed the LSVs to install the TRVs.
Therefore you need to re-balance them. Did you record their original settings?

I recorded their original settings, but I replaced the lock shields, and I've
no idea whether the number of turns are transferrable. Initially I set them
to be what they had been on the old ones, but I soon noticed it wasn't
balanced properly - hence doing a (basic) balancing.

Fair enough. They seem to vary from several full turns to just 1/2 turn from
fully open to closed.

In addition, Ed's points about the by-pass and the cylinder coil need checking
out. If you have no motorized valve or TRV on the cylinder coil, it must be
balanced with a series gate valve used as a LSV, just as if it was a radiator.
You can get 'locking' gate valves for this purpose.

The system has 2 motorized valves - one for heating and one for hot water.
When I balanced it, I did so with the water off. The water is only heated
for an hour or two morning and evening and wasn't being done when I did the
room temperature check.

That's fine. You only need to balance the DHW coil if it is to be on
simultaneosly with the CH, but I think a better system uses only one system at
a time, then each gets the full boiler output.

I did notice a small 15mm pipe with a gate valve on it which appears to
bypass the motorized valves. After being unhappy with the balancing I did
twiddle it a little and returned it to the same place it was set to before.
Should this be open or closed - or just adjusted? I assume its a safeguard
so that when both valves are shut and the pump/boiler is on, that there is
some flow back to the boiler? If that is the case, I guess it must be open,
but not enough to cause too easy a path back to the boiler.

Thats will be it. As you suggest its setting is somewhat hit and miss.
Basically it is an unsatisfactory solution and the proper way to do it these
days is to use an automatic by-pass valve. See this link for further

Whilst I didn't use any sludge remover before installing TRVs, I did remove
each radiator and flush it through thoroughly, so any sludge etc would only
be that in the pipework (or distubed at the bottom of the header tank when
it refilled).

Don't forget to add inhibitor to the CH water.

Thanks for the very helpful hints - I'll report back with the temperature of
the boiler output and I'll give the balancing a better go. I wasn't aware
before that the output pipe of the radiators should all be roughly the same.

Yes, a radiator is designed to give out its rated heat when it has a certain
specified temperature drop from flow to return, typically 11C. Getting them
all the same is the whole point of balancing.

Phil Addison
The uk.d-i-y FAQ is at
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