In an earlier contribution to this discussion,
Dave wrote:


One problem I has is that the boiler is switching off quite quickly. I
think the flow around the system is too small, so the boiler shuts
off. Of course this could be a boiler fault, but the fact the pump was
making a strange noise led me to believe that was probably not so.

I assume the boiler shuts off when the input temperature is above some
preset value. There is a control on the boiler, but it is marked 1, 2,
3, 4, 5 rather than any numerical value. I can check the manual for
the oil boiler and see if that indicates when it should shut off.

I assume that the boiler stat controls the *output* temperature - which you
can measure with your IR thermometer! Aim at about 80 degC. If the system is
not absorbing the full boiler output, the boiler will cycle on its stat.
This is quite normal. It doesn't matter if the flow temperature fluctuates a
*bit* during balancing because you will be measuring both sides of each rad
and determining the *drop*. It's important to keep the pump running all the
time.

I'll order some TRVs, as I have at least 4 which are showing some
signs of failure - usually the plastic becomes brittle, then the top snaps
off . Is there any one make you would consider better than others? I
noted that they seem to be available from about £7 to £90, with most
in the range £7 to £15. Cost is not really an issue, but I'm fed up
with the things going wrong. I was in fact warned their reliability
was not great, but the failure rate seems to be higher than I would have
expected. I think the ones I have are made by Honeywell.

The valves with probably the best reputation are Drayton TRV4's. You'll pay
silly prices in the High Street but can get them at sensible prices on Ebay.

Once I've got the new TRVs, I'll flush the system and try to balance
it. One problem I have here is that since I don't know the ordering
of the radiators, it will be difficult to adjust them in the order
starting at those closes to the boiler. I'll have to take a best
guess on this I think.

Don't worry about that - it's not the way I do it, anyway. Start with all
lockshields fully open and then turn down the lockshields on the rads which
have the *lowest* temperature drop regardless of their proximity to the
boiler. This will restrict the flow on these rads and force more water
through the cooler rads. It's an iterative processes, and you keep going
round until you get more or less the same drop on all rads. Then you look at
the *actual* drop - which ideally should be 10 or 11 decC. If it's
significantly more, you need to increase the pump speed and if significantly
less, decrease the pump speed (assuming it's adjustable!) - and then recheck
the balance.
--
Cheers,
Roger
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