Why is my gas likely to be costing so much all of a sudden?

QrizB

Looking at the photo of your IHD, the peak gas use of 1.71kWh was in the 5am-6am period.

What time is your heating set to come on? Is the clock on your timer correct?

vic_sf49

Is the room they're in upstairs, up to temperature, so the rads don't need to heat up?

Can't remember what actually temps the TRV settings equate to, but I'm sure an internet search will reveal the answer, or some knowledgeable folk will come along soon.

vic_sf49

Is your boiler somewhere cold, so a frost setting might trip in?

Or do you have pre-heat turned on, so domestic hot water is pre-heated? To disable mine, I press the eco button. I'd prefer to wait a few seconds longer for hot water, than have the boiler firing in the background. 

Edited to add, the eco setting on my boiler switches off, if there's been a power cut.

QrizB

vic_sf49 said:

Can't remember what actually temps the TRV settings equate to, but I'm sure an internet search will reveal the answer, or some knowledgeable folk will come along soon.

Also it varies by manufacturer, so make sure your search turns up the correct one!

grn99

I'm just wondering if you've got TRVs set low in the same room as a room thermostat, preventing or slowing the target temp being reached, whilst the boiler is firing, doing its best to satisfy the stat? To my mind we only need a single temperature control in any given space or there could be a "conflict". 

FreeBear

B0bbyEwing said: We have no tank of water. It's just a comb boiler. 

As for the TRVs on the rads themselves I actually turned them down. Instead of sitting at 3 for some they're actually now on 2.

Some combi boilers fire up at regular intervals to keep the internals hot just in case you need instant hot water. One or two like the Viessmann 111 have an internal storage tank (46l) to keep hot - Check to see if you have an Eco mode to disable the "keep things hot" function.

A hot water tap left running (or worse, a leak) would also account for the high levels of gas consumption.

Whilst turning TRVs down can help to save energy, they only really work if you have a lot of radiators and a boiler that can modulate down to a very low level - I have a Viessmann 050 which can modulate down to 3.2kW coupled with 9/10 radiators rated at a total of ~12.5kW, 7 with TRVs. I noticed that as the boiler modulated down (and running at a low flow temperature), when TRVs activated on some of the bigger radiators, the boiler would start to short cycle. This impacted significantly on efficiency and I wasn't really saving any gas (the cold rooms would also suck heat out of the adjacent ones). Leaving all the TRVs on max, the boiler runs for a shorter period without short cycling.

Scot_39

B0bbyEwing said:

That was what it showed. 

From maybe about 4-5pm today I turned the 2 rads in the living room off & the big rad in the kitchen off (off = to the frost setting) as I had the fire on.
By the time I finished watching a movie at 9:30pm that reading on the left said 22.xx kWh (xx because I can't remember the exact number).

Those 1/2 hrly numbers assuming the 1.71 kWh - a scale line or even if was the peak slot energy - so all points sub 3.4 kWh - are really low compared to a boilers peak burner power - more typically in the 20-30kW range.


Dont have gas now with smart meter resolution, but  could be something like anti frost rather than real heating or hot water tank demand.
Having seen others charts peak nearer 10kWh per half hour.

FrugaiMacDugal

What were the early morning outside temperatures on day of IHD display?

QrizB

Scot_39 said:

B0bbyEwing said:

That was what it showed. 

From maybe about 4-5pm today I turned the 2 rads in the living room off & the big rad in the kitchen off (off = to the frost setting) as I had the fire on.
By the time I finished watching a movie at 9:30pm that reading on the left said 22.xx kWh (xx because I can't remember the exact number).

Those 1/2 hrly numbers assuming the 1.71 kWh - a scale line or even if was the peak slot energy - so all points sub 3.4 kWh - are really low compared to a boilers peak burner power - more typically in the 20-30kW range.

They're hourly (24 bars per day), which only makes it more odd. I would suggest heating a HW tank but it's a combi boiler.

Maybe a hot tap not quite closed properly?

Scot_39

There are combi boilers iirc  with small local tanks they heat for instant hot water on demand.

Or as above a frost loop sensor drifting upwards perhaps.

One previous poster found theirs was so far off it ran in summer overnight.

My parents combi wouldn't actually react to a dripping or very low flow rate - at least initially - you seemed to have to open a fair flow rate to get it to fire up.  Never left it on a long term trickle to test though.  It's certainly an interesting question.