# Radiators cool down after an hour



## lucylu

We have a baxi multi-iheat 2.5Kw wood pellet in the Garage.

When we turn on the heating the radiators heat up hot to touch however after about 3/4 - 1 hour later they have cooled down and are lukewarm at best. In the past if you had the heating on for an hour you would have to turn it off now if it on for a couple of hours you wouldn't notice it.

We have 18 rads mainly small ones and house is 2000sq ft

Our plumber is not dependable when we contact him.Bleeding the radiators didn't make much of a difference.
Any ideas what the problem is ?


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## 3CC

Is your heating system controlled by room thermostats? If so, this would mean that the rads all get hot at first and then when the zone in which the thermostat is located reached the set temperature, the heating would switch off and the rads would cool down.

This would be perfectly normal.


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## lucylu

There are 2 zones 1 for upstairs and 1 for downstairs.

Changing the temp on the thermostat dial doesnt make much of difference.
Over the last few nights it is up to its last 22c the house never gets hot.


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## 3CC

A few questions?

1) When you turn on the heat at first, all the rads get very hot all over( ie both at the top and the bottom of each rad)? Correct?
2) When the rads start to cool down, do they all cool down around the same time, or all at different times.
3) I presume that you switch on different zones at different times. If so, does each zone heat up and then cool down separate from the other zone.
4) Do you have TRV's on each rad?


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## lucylu

Thanks 3CC

1) When you turn on the heat at first, all the rads get very hot all over( ie both at the top and the bottom of each rad)? Correct? Yes correct 
2) When the rads start to cool down, do they all cool down around the same time, or all at different times. They cool down around the same time however some would remain slightly hotter than others
3) I presume that you switch on different zones at different times. If so, does each zone heat up and then cool down separate from the other zone. no the heating goes on at the same time, there is just a thermostat upstairs and downstairs. downstairs thermostat is up higher than upstairs.
4) Do you have TRV's on each rad?  no TRVs


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## 3CC

Lucylu,

Given that the heating system comes on when you expect and works perfectly without any cold spots in your rads but then cools down after an hour, the only cause of this that I can think is that the rooms have reached the set temperature and thermostats are kicking in and locking out the boiler.

You could carry out a few little checks that would test this. 

1) You should hear a little click from your stat as you rotate the dial from 0 to max. Can you try this BEFORE YOU SWITCH ON THE HEATING in the morning to confirm that you can hear this from the stats.
2) Then, one evening when the heating has already come on and then cooled down, try the same test. If you do not hear any click when you rotate from 0 to max, the stat is the problem.
3) I would also be interested to know what happens if you switch on the downstairs zone say 2 hrs after the upstairs zone. It might help people understand better the issue.

Can I suggest you do the above and report back but I think the stats are suspect no 1 for me at present.


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## lucylu

thanks 3CC for your help I will give the checks a go..


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## lucylu

You could carry out a few little checks that would test this. 

1) You should hear a little click from your stat as you rotate the dial from 0 to max. Can you try this BEFORE YOU SWITCH ON THE HEATING in the morning to confirm that you can hear this from the stats. the dial never goes to 0 it is set to 10c and it clicks at about 15 c
2) Then, one evening when the heating has already come on and then cooled down, try the same test. If you do not hear any click when you rotate from 0 to max, the stat is the problem.the dial will still click on or off at 15c
3) I would also be interested to know what happens if you switch on the downstairs zone say 2 hrs after the upstairs zone. It might help people understand better the issue.when we turned downstairs back to 10 (off) upstairs heating was hotter for at least 2 hours and then it eventually cooled down, another day we tried it the opposite way around however downstairs radiators didn't get as hot as the upstairs rads .
both dials are siemens Landis straefa dials


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## Guest125

Just a suggestion, I wonder is the circulation pump continuing to run after the system is shut down thus "taking" all the heat?


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## lucylu

Thanks Caff
The hot water wouldn't be boiling either..


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## lucylu

thanks all for your help it appears that the pressure from the burner was not at the correct.

all snug again


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## Guest125

lucylu said:


> thanks all for your help it appears that the pressure from the burner was not at the correct.
> 
> all snug again



Low on water pressure? Make sure there's no water leaks.


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## Gary Bowditch

Hi, we have one radiator that cools down after 2hours... why


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## pudds

Gary Bowditch said:


> Hi, we have one radiator that cools down after 2hours... why



If you have a trv on it then it could be that the room temperature has reached the level that the trv is set at.


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## Wal12121

Hi I have similar problem, The radiators in my house when I turn the central heating on it only lasts for an hour or so and then cools down. I’ve checked my water pressure which is fine, in order to get the heating back on I have to turn the hot water alongside.I have also tried and bled the radiators.
Please any advice for this? thank you


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## roker

3CC said:


> Is your heating system controlled by room thermostats? If so, this would mean that the rads all get hot at first and then when the zone in which the thermostat is located reached the set temperature, the heating would switch off and the rads would cool down.
> 
> This would be perfectly normal.


thus could also happen with thermostatic radiator valves


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## Scarletw

I have similar issues, my boiler is Viessmann Vitodens 100-w, 4 zones, some 25 small rads, some were hot some were cold before, after the heating engineer replacing the pump, bleeding and balancing the rads, made things worse, the rads are warm to cold only switch the boiler off for a bit the turn it back on will get some rads Wormer.  The boiler burns, then cuts off. Can someone advise?


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## jpd

Get a better engineer?


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## Scarletw

Thank you jpd, I am unsure who to call at the moment, as already paid for £502 with no luck.  If someone would be able to pointing out the possibilities, at least I can expect what the better engineer would do next.


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