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 hot
as it used to be - even with the TRV heads off. I've also noticed a lot of
boiler cycling (old Baxi WM 531 RS boiler).
Previously the living room (large room with 2 radiators) used to get quite
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 toasty)
but that doesn't appear to make a significant difference. I did struggle to
get much of a temperature drop on some radiators - some only had as little
as a 3 degree drop with just a 1/8's of a turn on with the lockshield. The
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 were
about 5-8 degree drop.
The pump (UPS 15-50) is running on its slowest speed and always has done.
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) and
failed to make any difference to the temperature of the pipes to the largest
Specifically, with the boiler thermostat set to 3 (with 5 being highest) the
boiler would heat the water for
Boiler thermostat setting Pump setting Time boiler on
Time boiler off Pipe therm 1 Pipe therm 2
1 min 35 secs 1 min 45 secs 50
2 min 25 secs 1 min 20 secs 50
1 min 40 secs 1 min 45 secs 50
The pipe thermometer readings were from the large (9') radiator which was
the one which got cold when it wasn't balanced properly.
As you can see, the boiler is cycling about every 2 minutes and changing the
pump speed made little difference.
The radiators closest to the boiler do get hot and the downstairs radiators
don't get as hot, but are hot.
I've got a thermometer (built into a small travel clock) and I've yet to
make the temperature in the living room more than 20.5 even though I've set
the wall stat in the hall to anything up to 25. Note, I did these checks
with the TRV heads off - so they're not restricting the flow and I got the
same reading with both TRV's set to 5 (the highest on the Pegler Terrier
I'm sure the cycling times dropped when I changed the boiler thermostat, but
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 is
very quiet on speed 1 but becomes quite noisy on speed 3 (and its about 3"
away from a bed in a spare room - so I don't want to it be too noisy). I've
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 when
the TRV's are off and that the pump speed makes little difference to the
temperature and boiler cycling.
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