I’ve noticed since using the central heating this year that it appears to be taking ages for the house to warm up.

Its an 1930 stone semi, so isn’t the best in terms of insulation.

Its a combi boiler with Honeywell CM927 thermostat. The day temp is set at 14, which I am not sure if it drops to that or not. However it is currently set to rise to 20 from 3:30pm. Its now gone 6:30pm and its just reached 19 deg.

Is that normal for house to take so long??

I wondered if the thermostat cycle rate may be wrong, or the external temp sensor on the boiler might be thinking its warm and not using full heat from the boiler? The boiler appears to be reaching about 49 deg before stopping firing up.

Any ideas? Is it just that I live in an old house, and Ive foggoten how long it takes to heat up 🙁

That sounds way too slow. We have a 30s house too with solid walls and a lots of fresh air getting in. Heating comes on at 5.30. Up to temp in well under an hour.

1911 here. House is usually warm within 15mins.

Maybe it’s haunted 😯

It’s not your CH that’s the problem it’s the lack of insulation. If the radiators are warm to the touch the CH is working.

When we bought our 30s house it took a long time to warm up and a very short time to cool down. The heating went off at 10:00 at 18°C and by the middle of the night we’d hear the heating come on at the lower 14°C setting. By the morning the temperature was down to 12°C without the heating. After insulating we removed the central heating and use the wood burner in the evening. If we heat to 21°C in the evening it’s still 18°C the following evening, one burn adds about 2°C.

1900s mid-terrace here.

Time taken is very variable. In the rooms with modern floor-to-ceiling panel rads in them it is PDQ.
In the rooms with elderly single rads it can take a good half hour to feel any benefit.

/I assume you’ve checked the time on the timer //

also that the thermostat is set right – we had a longish power cut the other day, and found the hall stat had reset to – 20/21 deg No wonder the house was toasty (and I’d come in from heat shed..) It’s usually about 17..

Check CH water temp dial in case temp is too low. Lukewarm central heating is more efficient but takes longer to heat the house.
Check rads are uniformly hot, cold bottoms = sludge, cold tops = airlocks.
Check position of stat, is the room its in heating up quickly and making the boiler cycle on and off before the other rooms have got to temperature?

Ours came on a couple of weeks ago, should be warm by June.

I’d have thought a minimum of 60C at the boiler for heating (and efficiency)
If you can control the two independently >60C for the heating and 60C (max) for the water

Get a nest thermostat. It will work out the timings for you unlike a traditional thermostat. You just tell it the time you want it a certain temperature by. Our heating bills have dropped since having ours because it takes away all the guess work. Also worth considering is raising your base temperature from 14. Ours is set to not drop below 18 and when we are in it raises to 20. By doing this you are just topping the heat up instead of starting from cold. If I look at the chart nest generates our heating comes on a few times in the day and night for a few mins to keep it at 18. But it then takes a lot less time to get it up to 20. Not sure how well this would work in an inefficiently insulated house but it may be worth trying.

Although not a Nest, the Honeywell does the same learning thing. In that mode fuel bills went up massively as it was having to switch on hours before needed 🙁

Last night I rang British Gas who are offering free cavity insulation at the min only to be told our house has already had it done !

I might have to try keeping the heating at a higher low setting and see if that works…

Are rads full? We had a house where they needed bleeding every couple of months or they were full of air…

Yep all working correctly.

Even wondered about letting some smoke bomb things off in the house to see if I can identify any big draughts

Ours has taken an over anhour this morning to raise the temp from 14 to 17 degrees. It’s the outside temp drop that’s causing it. Last week it was 12-15 degrees through the day, today it’s 4…

If it’s insulated and taking that long to heat up the rads are way too cold. We’ve got a Victorian semi that’s fairly exposed and no cavity insulation and could be described as well vented.

It gets up to temperature in half an hour from cold. New combi boiler a couple of years back and all rads are 15-5 years old with TRV’s.

Soumds like one of the following causes: Crap rads that are under specified for the rooms; Rads full of sludge/air; Water temperature too low; boiler under specified.

Edit: what’s the humidity like. It takes longer to heat up a damp house.

Tried speeding up the pump on the boiler ? Some are 3 speed and a faster setting might improve things . It also might not.
Apart from that , damp air . Is there an extractor in the bathroom ? Is your washing allowed to dry over radiators every day?
My 2 bed flat will easily go up by 1’C per hr with a 24kw combi. Cavity walled but not filled with polyballs .

is there a suggestion here that lower temp in the rads is more effcient? Our semi albeit 1906 victorian heats up very fast at 20 to 30 mins and the thermostat sits at 20 summer asnd 18 winter with no heating on.

Should I be tempted to lower the rad water temp?

Tried speeding up the pump on the boiler ?

I’ve have kind of wondered if it could be that the thermostat isn’t triggering the boiler often enough. How do you work out the correct cycle rate for your boiler?

What boiler is it? If its only getting to a 49 degree flow temp and you have an external sensor the curve on the weather comp could be set wrong…

Lower water temp will be more effcient with a modern boiler the lower the return temp the better as it will help the boiler condense more, Anything below 55c give or take a few

Its a Viessmann Vitodens 100

From reading the installation guide the weather comp graph is controlled by the temp dial on the front of the boiler… which sounds a bit odd?

Moved it from 4 to 5 last night and now boiler temp getting to 62 ish

Maybe I now need to fine tune it down to 55deg?

However surely any change in external temp means I will need to adjust that, which defeats the object?

No. Theres a curve that the boiler follows according to the settting you have put it to. That needs adjusting to the installation. Sometimes its set too low. Sometimes too high.

62 will be fine as thats the flow and you will have a lower return temp than that.

You’re just going to have to fine tune it a little. But once set to you house shouldn’t need adjusting in the future.

Well I went from 58 to 54 earlier. The house dropped to 20 – it’s set to 21 – and it’s been hovering at 20.5 ever since with the boiler going continually. I haven’t touched the Rad valves. How’s that saving me money? 😐

Ghost House! 😮

(in the tone of Peter Griffin saying Road House)

I read some time back some advice suggesting just leave the heating on and use of room thermostats actually can cost the same or less than having the boiler work hard heating a house from cold every day.

Tried that, and sure enough I’m not paying any more at least, and my house is always warm.

Once warm, the boiler is just heating in small bursts to bring temperature back up to the thermostat temp.

It’s also better in freezing conditions to have some heat in the pipes, not have them freeze while you’re out of the house or overnight.

deadkenny…I still don’t buy into that.

How can the boiler cycling on and off during the 10-12 hours I am out of the house be cheaper than a 1hr blast at 6pm followed by an hour or so of cycling on/off.

A house will leak more heat at 20c than one that is allowed to drop to say 16c whilst you are out.

Last winter my boiler was on for 1.5hrs a day, supplemented by the stove in the evenings.

Insulation is key. It will rarely cycle on and off as the heat is being kept in. The cycling all day can be equivalent or less than an hour’s burn (or more as people often set off at night and a burn in the morning from very cold).

If the system lets you set a lower temp but not off during the day, then it may only come on a couple of times during the day as the temperature takes ages to drop, and then a short burn to bring it back up when home in the evening.

If it’s insulated well enough then heat loss should be pretty constant. So, put a timed stat in. I did many years ago. House isn’t allowed to get cold enough to need 2hrs of full blast heating twice a day. It’s more comfortable to boot. Costs me no more than heating from scratch twice a day. Ours is an ex Council semi with solid walls, but we had solid wall insulation put in a few years ago. Made a massive difference.

Typical old fashioned approach, turning it off & on all the time. I remember visiting someone in New York many years ago. Their house didn’t have rads. It had skirting boards with a finned heating pipe inside. The house was very well insulated. Heating comes on in October/Nov & off in March/Apr. Their house was lovely & warm all the time. They found it quite odd that we actually turn the heating off during the winter.

Kryton.
If you have a modulating boiler you were probably using less gas.
Think of it like cooking a large pan of pasta . You use say 3/4 power to get a rolling boil, however once there you can wind the heat on the hob down to minimum and the water still simmers away.
a modulating boiler will do the same. Full chat to get the ciircuit hot , then reduce flame to hold. To a point of overheat , then it has to switch off .
So although the burner was on it may , possibly have been usinh half the gas , but the fan and pump run and make all the same noises .
Some modern combis can moodulate as low as 4kw output . So split between 5 room that is less than 1kw input per room .
If you have a modulating boiler. . . . . .

I fitted a Nest earlier in the year (and it works very well) but I see they’ve just released a version 3 that does the hot water as well. 👿

Radiators don’t fill with air as the system is under pressure. They fill with hydrogen, which is a by-product of oxidation inside the steel rads. This happens because the system doesn’t have enough inhibitor added.

If it is taking so long to heat up the house, even though the radiators are all air and sludge free, chances are the radiators are under sized.

Each radiator should have a btu output matched to the size of the room, and the whole system matched to the size of the house. A system that is under sized will take forever to warm the house to the desired temp, and if its badly out, it will never get there.

Radiators don’t fill with air as the system is under pressure. They fill with hydrogen, which is a by-product of oxidation inside the steel rads. This happens because the system doesn’t have enough inhibitor added

Possibly, but theres always the argument that the system doesn’t need inhibitor and just the right ph level

Also theres a chance on an open vent system pulling air into the system. Not necessarily hydrogen.

Kryton.
If you have a modulating boiler

Every day is a schoolday. Apparently I do – valiant ecotec plus 831 with “advanced modulation” ratio 1:6 no less. Lucky me. So the house did take longer to warm this morning which of course is due to lower rad temps, but I guess I’m better off in the long run with a min 5kw usage, cheers!

I’m not convinced… The house never got to temp on the thermostat yesterday, meaning everything was running far more than usual. I’m going to give it a couple of days as the outside weather returns to 9 degrees rather than the 0 it has been this weekend for balance, but surely reaching temp and switching off for the sake of 4 degrees at the boiler end of things must be more economical.

Id get an hearing engineer to check the system, you had it serviced regularly? Just a thought

OP, perhaps you should re-read your O&M manual again.

When you replaced your boiler, did you also replace your radiators? If not then I’d assume your system was designed on pre-condensing operating temps (i.e. 82 deg C F/71 deg C return). These days boilers designed to run at 60/40 (or even 50/30). This means that the radiators need more surface area to give out the same heat (i.e. old average temp was ~76 deg C and room temp of, say, 21 giving a ‘delta’ T of ~55 deg C. With condensing its reduced to only ~25-30). The lack of heat in the house (and low flow temp) would lead me to think this is the issue. Boost the supply temp, see what happens. You can run it at 80 deg C without any problem (it won’t condense though, so less efficient). Heating is designed with a region specific external design temp. Down in the South its around 0 deg C (up here, in the frozen scottish north-east, its -5 deg C) so guess it was pretty much near its design these last couple days.

Which brings me to the other thing. A condensing boiler is more efficient at low load (the OP’s boiler is 97-98% efficient at 30% load) than at full load (OP’s is only ~88% at full load). so ~10% more efficient just ‘topping’ up. Whether this offsets the ‘additional’ heat delivered to the house overall depends on what is being lost when keeping the house warm all the time (instead of heating intermittently) I don’t know. Don’t have the thermal modelling software to check that out.

Metal heart – thanks for the info… I think from what I understand.

It was a full new installation 6yrs ago, rads, boiler & pipework. Hopefully the guy who did it knew what he was doing ?!?

Turned the dial up from 4 to 5 two days back. Boiler temp now says 50, not 40.

Changed thermostat to on all day at 15. And rise to 20 thirty minutes early than previously. Walked in to the house at usual time tonight and temp at 19 which is a very slight improvement but not great seeing as though that will have used more gas in every way!

Might even get a Viessmann engineer out to see if they can work out what’s happening….