Radiators red hot but give off little heat

[jonnybegood]

I am not an expert on central heating systems so looking for some advice as to what to do next.
I bought a property approx 2 years ago with a 4 year old combi boiler fitted in the attic, the boiler works well heating all 12 radiators in the property with no problem at all, I think the boiler is rated 31Kw.

The radiators in some of the rooms look fairly new, with the fins on the back and the grid on the top, all but 2 have TRVs and there is a room stat in the hallway.

Now I have been wondering about the radiators as the property takes a long time to get up to temperature and having done a BTU test it seems 1 or 2 of the radiators will require changing due to the size of the rooms.

However a number of rooms have radiators more than adequate but they never seem to heat the rooms completely even though we have Cavity wall insulation, roof insulation and double glazing.
The radiators are red hot to touch but if you stand 5cm away you can feel no heat at all coming off them, my parents property is of similar size and they have smaller radiators but when you walk past them you can feel the heat coming off, in their rooms the radiator can be on for 30mins and you need to turn it down, however there seems to be no heat coming off mine even though to touch they feel just as hot as my parents radiators.

Any advice on what could be causing this lack of heat off the radiators?

Forgot to add, its the same if you hold your hand 2cm above the radiator, you can feel a bit of heat but nothing at 5cm unlike my parents that really pump out the heat.

 

[mogget]

Any advice on what could be causing this lack of heat off the radiators?

Because it's been b****y cold the last couple of months?

Seriously though, heating systems are designed for a particular outside temperature - usually -1 or -2C I think. It's been much colder than that lately and if the radiator / boiler sizing is a bit marginal this might cause problems.

Have you closed any trickle vents, made sure outside doors are draught-stripped etc?

What setting is your boiler thermostat on?

 

[swbjackson]

Have you felt all over the radiator? Run your hand over the whole radiator and make sure it is hot all over.

Mike

 

[steve32]

how many hours a day is the heating on for, is it an old house or new are the fins on the radiators clean not full of dust or fluff
are curtains above rads or furniture in front to prevent air flow

 

[jonnybegood]

What setting is your boiler thermostat on?

Since we had the room stat fitted the boiler stat is on maximum - Approx 85 - 90 degrees

Have you felt all over the radiator? Run your hand over the whole radiator and make sure it is hot all over

A few are very hot in the middle and top, but get cooler towards the bottom, the others are hot all over
I have bled them all this winter, could there be sludge or other crap? How best to tackle this if it is the problem.

how many hours a day is the heating on for, is it an old house or new are the fins on the radiators clean not full of dust or fluff
are curtains above rads or furniture in front to prevent air flow

5 hours a day, 8 hours on weekends, its a 1960s property.
No furniture in front, curtains never closed but I suppose the fins could all do with a clean, does it affect them that much?

 

[swbjackson]

Could be sludge in the system. try balancing the radiators first.

Mike

 

[bengasman]

most rads need to be 150 mm above the floor and a little away from the wall to work properly

draft caused by ventilation openings, open chimneys and leaky doors windows can cause enormous heatloss

to test rads, you need to feel along the bottom at various places; if you find that anywhere between the valves is colder than near the valves, you system needs cleaning

 

[D_Hailsham]

I suppose the fins could all do with a clean, does it affect them that much?

A 600mm high x 1000mm wide radiator with fins produces about 1kW heat; without fins it produces about 600W. So, yes, the fins are important. All you get, without the fins, is mainly radiant heat (what you can feel when your hand is near the radiator) and some convected heat; adding the fins increases the convected heat considerably.

Clean all the dust etc out of the fins.

 

[jonnybegood]

Thanks for all the advice, I will have a go at balancing the system tomorrow, some of the radiators are hot all over whilst others cooler on the bottom.
So maybe now is a good time to get it cleaned or flushed I think the correct term.
How long does a good flush take and how much is a typical price for a 12 rad sealed combi system.

Do the majority of plumbers undertake this type of work?

 

[gas4you]

For a 12 rad system, flushed properly, I think it would cost very approx £500 ish.

This will vary in different parts of the country.

You could drain down, add X800, re-fill and run system for up to 3 hours, drain and flush through with cold mains from the filling loop your self.

A lot cheaper and if done right just as good.

Powerflushing can be very good, but is not the miracle answer that many try to say it is.

 

[jonnybegood]

For a 12 rad system, flushed properly, I think it would cost very approx £500 ish.

This will vary in different parts of the country.

You could drain down, add X800, re-fill and run system for up to 3 hours, drain and flush through with cold mains from the filling loop your self.

A lot cheaper and if done right just as good.

Powerflushing can be very good, but is not the miracle answer that many try to say it is.

Right I am going to clean the system and then re balance.
So here I need some guidance please.

My combi boiler and filling loop are located in the attic, my furthest rad from the boiler on the ground floor has a drain point, here is my plan, does it sound ok.

I will use X400 instead of the X800, it seems better suited to what I want to achieve.

1) I will add this to the full system at the filling loop and leave in the system for a week or 2 with all valves open. (Will this be ok with the pump etc when it starts to dislodge the sludge)

2) I will completely drain the system a week or 2 later using the drain point furthest away from the boiler on the ground floor

3) once drained I will leave open the drain valve and flush the system with cold water using the filling loop (I assume I leave open all valves on the rads etc).

4) Once the clean water has run through the system, close the drain valve and fill the system until pressure gets up to 1 bar

5) Add X100 at filling loop

5) Bleed all rads

6) Balance the system

Does this sound about, any tips or further advice?

How are the chemicals added at the filling loop, is there a way without getting water everywhere?

 

[D_Hailsham]

Right I am going to clean the system and then re balance.

I will use X400 instead of the X800, it seems better suited to what I want to achieve.

It would be better to drain the system and flush through with cold water before adding the X400. Flush until water runs clear.

Leave the X400 in for about 4 weeks before draining and flushing.

The problem with leaving all valves open is that the water will always take the easiest path, so some pipes and radiators may not get much flowing through them - particularly if they are blocked. Shut of all rads except one at both valves and allow the water to flow through the open
rad for 10-15 minutes (you may have to turn the boiler temperature down) then close that rad and open the next. then on to the next rad .... Start with the rad nearest the boiler. If there rads are on two or more branches, do one branch at a time.

X100 and X400 can now be bought in concentrated form suitable for injecting via a radiator bleed valve using a sealant gun or as Rapid-Dose, which is an aerosol based system.

Balancing Procedure

 

[Bambergaspipe]

I am not an expert on central heating systems

the boiler works well heating all 12 radiators in the property with no problem at all, I think the boiler is rated 31Kw.

Now I have been wondering about the radiators as the property takes a long time to get up to temperature and having done a BTU test it seems 1 or 2 of the radiators will require changing due to the size of the rooms.

uh- oh

However a number of rooms have radiators more than adequate but they never seem to heat the rooms completely even though we have Cavity wall insulation, roof insulation and double glazing.

And

The radiators are red hot to touch but if you stand 5cm away you can feel no heat at all coming off them, my parents property is of similar size and they have smaller radiators but when you walk past them you can feel the heat coming off, in their rooms the radiator can be on for 30mins and you need to turn it down, however there seems to be no heat coming off mine even though to touch they feel just as hot as my parents radiators.

Stand 3cm away

System may need balancing which most fitters can`t be bothered doing, look into it or look it up on this site.

 

[steve32]

i would suggest that 5 hours a day in a 60s house at this time of year (winter) is not long enough
i normally set systems up for a min of 3 hours morn 8 hours evening and from watching the weather forecast i would suspect this part of england is milder than your part
depending where your room stat is located i set them for 22 lounge 20 hall
try leaving heating on for min 12 hours for next 4 days once the structure and furnishings have warmed up you should notice a difference if not you may need to follow advice as above.
it will all so help to monitor room temp

hope this helps

steve

 

[D_Hailsham]

i would suggest that 5 hours a day in a 60s house at this time of year (winter) is not long enough

May be not, if the house did not have cavity and loft insulation and double glazing - see first post. Though there may not be enough loft insulation and the DG may be metal or wood, we don't know.

try leaving heating on for min 12 hours for next 4 days once the structure and furnishings have warmed up you should notice a difference.

I agree about getting the structure up to temp. My house (late 80's) is cavity and loft insulated (but only about 75mm) and u-PVC double glazed. The day time temperature is set to 21°C all day (home all the time) and the heating goes of at 10.30pm and comes on for 6.30am. The overnight temperature has not dropped below 15°C since we turned the heating on in September, despite outside temperatures dropping below zero. So the heating just has to raise the temperature 6°C each morning. A min-max thermometer is very useful!