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Central heating effectiveness
smart51 - 23/11/15 at 06:23 PM

The central heating in my house has been on for an hour and a half. It is 0 degrees outside and the thermostat is set to 22 degrees. The boiler is idling and saying the water temperature is 58 degrees and the radiators are hot. The house is well insulated and has an EPC rating of band C. Yet thermometers in the house are reading 16 degrees. Why is the house not really warm?

arrow-engineering - 23/11/15 at 06:44 PM

is the thermostat you are reading in the same place as the boiler? the boiler makes its own local heat, so if it has an onboard thermostat it will read different to one elsewhere in the house, height also has an effect on the reading

smart51 - 23/11/15 at 06:56 PM

quote:
Originally posted by arrow-engineering
is the thermostat you are reading in the same place as the boiler? the boiler makes its own local heat, so if it has an onboard thermostat it will read different to one elsewhere in the house, height also has an effect on the reading


No, the thermostat is on the landing and the boiler is in the bathroom.

macc man - 23/11/15 at 07:19 PM

Do you have trv valves on the radiators. Try adjusting them. The room stat could be faulty. Boiler stat may be faulty. Might be worth getting a service done before the weather gets worse.

BenB - 23/11/15 at 07:39 PM

Has the lagging fallen off runs which go via the basement? That does the job quite nicely!!! Check the temperature out of the boiler and the temperature going into the radiators.

We had issues today at work- just a shed load of sticky pin valves on the TRV. That was fun. Trying to unstick the pins and wrench the flipping electric heaters people were over-heating the rooms with (above the pre-set TRV temperatures).... "well I have to have the heater on because the radiators not working"....

big-vee-twin - 23/11/15 at 07:43 PM

Water flow temperature far to low radiators are designed to have a mean temperature to room difference of 50 degrees.

So if you want 21 degrees mean temp of rad needs to be 71 degrees.

So flow temperature 82 return temp 60 giving mean temp of 71 degrees.

58 flow temp will mean you are only getting about 50% of the radiator output.

will121 - 23/11/15 at 07:54 PM

quote:
Originally posted by big-vee-twin
Water flow temperature far to low radiators are designed to have a mean temperature to room difference of 50 degrees.

So if you want 21 degrees mean temp of rad needs to be 71 degrees.

So flow temperature 82 return temp 60 giving mean temp of 71 degrees.

58 flow temp will mean you are only getting about 50% of the radiator output.


As above boiler flow to low to get a good heat output, do you have a low and high setting on boiler? At low mine is 60 deg and 80 on high, only issue is it use to 'kettle' when on high untill I replaced pump so I ran it on low and had to leave heating on all day to keep heat in it, now on high heats house from 16 to 20 when 4 outside in about 30 mins

hizzi - 23/11/15 at 08:15 PM

what kind of boiler do you have? combi or one witha hw tank? if combi then you need to turn boiler stat up most likely. if you have a tank system it could be stat, pump setting,balancing, bypass valve lots of things. if its a tank system try turning off the hw and see how it behaves, if the hw isnt balanced then it will rob the heat until the tank reaches temp then the rads will come up

smart51 - 23/11/15 at 08:18 PM

Thanks everyone. TRVs are OK as all the rads are mad hot. We have a newish combi boiler which was recently serviced. I've turned the water temp up from 3 to 4 (out of 5) so we'll see what that does. In the last hour, the room temperature has gone up from 16 to 17.

hizzi - 23/11/15 at 09:09 PM

any more issues post the model of the boiler. many can be turned up internally for heat output these days. for instance glowworm boilers can be factory set to half their capability

Irony - 23/11/15 at 10:31 PM

If your radiators are hot then the boiler is working fine. Either your house is 'under radiatored' or the heat is escaping somehow. Do you have cavity wall insulation? Loft Insulation? Both can be gotten free from British Gas even if you are not a customer. I did so I know you can. Double glazing, or better double glazing? I would think about making your property more energy efficient before thinking of boiler issues.

Sam_68 - 23/11/15 at 10:31 PM

quote:
Originally posted by smart51...all the rads are mad hot.


If that's the case, then logically, either:
a) The rads are not transferring heat to the air around them (against the laws of physics, so unlikely)
b) The system has been designed wrong and the rads are under-sized and/or badly positioned, or;
c) The building is losing more heat than assumed by the heating design (and is therefore losing heat almost as fast as the radiators are putting it in, even at lower temperatures); see item (b).

If the rads are 'mad hot' but the room temperature is still not rising, then the problem is not with the function of the boiler, C/H system or controls, but rather that their capacity is inadequate to match the rate of heat loss from the building.

Is it a new build? Is it your first winter in the place?

Is it high or low thermal mass construction (U-values are only only one half of the equation; they will tell you the steady state rate of heat loss, whereas it's thermal mass that is more relevant in terms of response to changes in temperature/heating)?

Unfortunately, we'd need a lot more information on both the heating system and the house to stand a chance of pinning down the problem more accurately.

EPC's are not worth the paper they're written on, by the way.

craig1410 - 23/11/15 at 10:47 PM

The quickest way to lose heat is via draughts so maybe check that your over-window vents are not all wide open. Also check the cat flaps, letter boxes, loft hatch etc.

Also check that you've not just got a broken thermometer and a dose of the Flu!


[Edited on 23/11/2015 by craig1410]

mark chandler - 24/11/15 at 01:45 AM

It does sound like you need to insulate.

We bought our 80's house three years ago, first night in January heating flat out, radiators hot and you could see condensation in our breath, after a couple of days things improved as the house warmed up @ £150 a month gas averaged over the year.

We now have a combi boiler with correctly sized rads, approximately 50% larger as most of our neighbors have. Turns out it was a fixed price contract plumber so he went cheap.

We did loft insulation, pulled out 3" depth of fibreglass and install 12" wool, double glazed and had the free government cavity wall insulation.

I am typing now, although the heating went off at 10pm it's still to hot to sleep, we now do £50 a month in gas averaged over the year.

hizzi - 24/11/15 at 06:28 AM

rads mad hot doesnt mean anything, measure the temperatures. what is to hot to put you hand on doesnt mean they are at the correct temp.
you say your house is well insulated, so go and use a radiator calculator and check the sizes

smart51 - 24/11/15 at 07:15 AM

The room temperature hit 19.7 just before the timer clicked off. Now that the boiler is turned up, we'll see if it heats up quicker tonight. I suspect the house may be under radiatored.

russbost - 24/11/15 at 09:16 AM

It rather depends what temp you are starting from, I doubt most systems would go from 0 up to room temp in much less than several hours (not actually suggesting your house was at 0 to start with ).

What you are seeing with the boiler idling is normal, once rads are up to temp, boiler will idle until there is another call for heat which may be a further 10 minutes or so for rads to cool a little, set the system to come on 1/2 an hour or an hour earlier when temps are really cold outside

You may also need to increase thermostat settings as although that doesn't seem entirely logical, after all if the stat is set at 20 degrees or whatever that's 20 degrees??? BUT when much colder outside your losses are faster & rooms will feel colder without increasing stat setting by a degree or so

Also well worth checking round windows & doors for draughts as a draught when temp is 8 or 10 degrees outside won't have anywhere near as much effect as when it's freezing!

Sam_68 - 24/11/15 at 09:44 AM

quote:
Originally posted by russbost
It rather depends what temp you are starting from, I doubt most systems would go from 0 up to room temp in much less than several hours


And this will depend partly (primarily, on modern buildings with good levels of insulation and airtightness) on the thermal mass that I mentioned above.

You can have two buildings with identical U-values (insulation levels), but dramatically different response: a building with high thermal mass (dense brick/block/stone) construction will have a slow response, as the structure itself absorbs a lot of heat as it warms up, then releases it slowly as it cools down. A building with low thermal mass (timber frame or SIPs panels) will have a very fast response, and warmup/cool down much more quickly. In other words, thermal mass acts as a 'damper', to slow down and moderate internal temperature changes. Then there's the matter of whether the thermal mass is located inside or outside of the insulation layer, but let's not further complicate things!

You need to program you central heating accordingly: don't expect a high thermal mass building to be toasty warm half an hour after switching the heating on.

It can reach the point where, to get the temperature to a habitable level over short periods (in the evening, say, if you are out at work all day), you need to leave the central heating on continuously, at a low level, so that it doesn't have so far to 'boost' when you get home; otherwise, the thermal mass (and other losses) will mean that the heating system is only just capable of ramping the temperature up to a comfortable level just in time for you to switch it off and go to bed!

Mr Whippy - 24/11/15 at 01:05 PM

^ exactly as above, my heating is on all the time on a very low power (electric) as you have to mind everything in the room will hold the heat including the walls and this all takes time to settle. My house is a constant 18 degs +- 0.5 deg! (low for me cos babies need lower temps than adults), most of my heaters are just trickling out heat, just enough to balance the houses heat loss which is quite low anyway.

Irony - 24/11/15 at 01:14 PM

What they said^^^^^^^^

There are to two schools of thought. One is where you heat the house when you need it and turn it off when you don't. The other is you keep the property at a certain temp and keep the heating trickling out heat to maintain this level. It depends on your property. It is possible to insulate your house on the outside and then rerender which would mean your house has a high thermal mass, once it was warm it would stay warm but the temp won't change from cold to warm quickly.

I live in a bungalow and the first winter it was uninsulated and didn't have cavity wall insulation. In a bungalow the roof space is huge and the house literally needed the heat on all the time. After insulating it has made a big difference.

big-vee-twin - 24/11/15 at 06:21 PM

You can scald your hand at around 45 degrees so mad hot to your hand is not hot enough for a radiator to function correctly at 80 degrees

smart51 - 26/11/15 at 05:25 PM

I turned up the boiler and since then it is heating up the water to around 68°. The radiators are around 8° to 10° cooler and the rooms are reaching 19° a lot more quickly. That said, it is a lot milder outside so the system is having to do less work. We'll see what happens when it turns cold again. Thanks for the advice.