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David Hearn
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Default Another heating problem question!

"Ed Sirett" wrote in message
On Thu, 11 Dec 2003 18:43:55 +0000, Tony wrote:

Don't know what kind of TRVs you've got, but on my old house if we

wanted a
radiator to get super-hot, we had to unscrew the top unit of the TRV a

turns. Even though they were fully opened, it seemed that the valve was
partially closed and only the unscrewing made them fully open.


"David Hearn" wrote in message
I added TRVs this weekend and the week before replaced the boiler
thermostat. Since doing this I've noticed that the downstairs is not

as it used to be - even with the TRV heads off. I've also noticed a

boiler cycling (old Baxi WM 531 RS boiler).

Previously the living room (large room with 2 radiators) used to get

hot with the heating on - now it gets warm, but not warm enough really.
I've tried rebalancing (which previously got the downstairs nice and

but that doesn't appear to make a significant difference. I did

get much of a temperature drop on some radiators - some only had as

as a 3 degree drop with just a 1/8's of a turn on with the lockshield.

highest drop appeared to be on the largest (and furthest radiator which
isn't getting quite as hot) which was 20. The majority of the rest

about 5-8 degree drop.

The pump (UPS 15-50) is running on its slowest speed and always has

Anything more than this and there's a noticeable noise from the
pump/pipework. I did a test last night and increasing the pump speed
altered the boiler cycling times only slightly (5 seconds different)

failed to make any difference to the temperature of the pipes to the

downstairs radiator.

Specifically, with the boiler thermostat set to 3 (with 5 being

boiler would heat the water for

Boiler thermostat setting Pump setting Time boiler on
Time boiler off Pipe therm 1 Pipe therm 2
3 1
1 min 35 secs 1 min 45 secs 50
5 1
2 min 25 secs 1 min 20 secs 50
3 3
1 min 40 secs 1 min 45 secs 50

The pipe thermometer readings were from the large (9') radiator which

the one which got cold when it wasn't balanced properly.

As you can see, the boiler is cycling about every 2 minutes and

pump speed made little difference.

The radiators closest to the boiler do get hot and the downstairs

don't get as hot, but are hot.

I've got a thermometer (built into a small travel clock) and I've yet

make the temperature in the living room more than 20.5 even though I've

the wall stat in the hall to anything up to 25. Note, I did these

with the TRV heads off - so they're not restricting the flow and I got

same reading with both TRV's set to 5 (the highest on the Pegler


I'm sure the cycling times dropped when I changed the boiler

I'm confused that increasing the pump speed makes little difference.

What sort of noise would you expect from my pump on speed 3? The pump

very quiet on speed 1 but becomes quite noisy on speed 3 (and its about

away from a bed in a spare room - so I don't want to it be too noisy).

checked that the system has been bled properly including the pump.

I'm going to continue tweaking the balancing of the radiators - but I'm
puzzled that it used to get uncomfortably hot but now it doesn't even

the TRV's are off and that the pump speed makes little difference to

temperature and boiler cycling.

It is likely that the old failing thermostat was effective set quite a
high output temperture to the boiler.

Is it possible that the water heating coil is taking all the flow away
from the heating circuit - is there any control on this?

Seems to me that there must be quite an easy path for the water to avoid
going to the big rad.

I wonder if turning off all the rads except the big one one would make any
difference? i.e. all the heating is going through the coil and/or bypass

The water heating is separaetely controlled and wasn't turned on during the

I did twiddle a lockshield in the hall today (turned it from 1/2 turn to 1/4
turn I think) and this evening the living room felt quite a bit warmer and
the room temp appeared to reach 21.4!!! I'm thinking its probably just a
balancing thing.

Incidentally, I'm sure I can hear a bubbling noise from the boiler towards
the end of its heating period - and that's with a thermostat setting of 3.
I've turned it down to 2 now to see what happens to the room temp. It most
certainly does seem that this thermostat is working differently to the old
one. The old thermostat was marked 106 oC and this new one is marked 90oC -
but as people said before, 106oC is above boiling point, so it may not be a
reliable figure.

Anyway - thanks - I think I'll just try a little more twiddling (including
turning off all the other rads and seeing what happens).