Not enough Heat

[Wagger]

We have recently had oil fired central heating installed.
All radiators have TRVs. We also have a system thermostat inthe hall, set at 25 degrees.
When the heating is first switched on all radiators becomehot or very hot but our rooms and the main thermostat reach only 19/21 degrees.After around 2 hours the radiators furthest from the boiler start to cool andwhile they warm up intermittently the rooms never get above 19/21. All TRVs areset at 5.
The system has been balanced and we are satisfied that thisis not a boiler problem. Our plumber is stumped. Any ideas?

 

[rpm]

Can`t help I`m afraid, but thanks for registering and welcome to the forum Wagger.

 

[stevetheplumber]

i would disconect the room stat and see if the rooms get hot then if they do its a romstat positioning problem if they dont its either rads pipework or boiler to small

 

[joni os]

If not the room stat. Is your boiler modulating correctly.

 

[ShaunCorbs]

if boiler is still fired and furthest rad is cold not the room stat

 

[snowhead]

Was the system designed (radiator sizes and boiler size) to work at 25 degrees?

Is 5 the maximum on the TRV?

Is the boiler cycling on and off when the temperature is 19 / 21 or is it running continuously?

 

[Wagger]

Thanks. It looks wired in and I don't know how to disconnect it. However, the stat has been replaced and made no difference. We also tried increasing the temp with a hair drier and were able to do so. Of course, it could be a problem with the connection as the stat is wired into a complicated box and I don't know what is happening in there.

 

[Wagger]

Thanks Snowhead. Answers : I don't know for certain but it should be OK . However, I suspect in some rooms the radiator may be too small although not in others where ther is the same problem.
Yes 5 is the max.
Boiler is cycling on and off when at 19/20

 

[Wagger]

Sorry Joni os, I'm not an expert I don't know what you mean by boiler modulating.

 

[Wagger]

Thanks ShaunCobs. I'll check that out.

 

[doitmyself]

We have recently had oil fired central heating installed.
All radiators have TRVs. We also have a system thermostat inthe hall, set at 25 degrees.
When the heating is first switched on all radiators becomehot or very hot but our rooms and the main thermostat reach only 19/21 degrees.After around 2 hours the radiators furthest from the boiler start to cool andwhile they warm up intermittently the rooms never get above 19/21. All TRVs are set at 5.
The system has been balanced and we are satisfied that this is not a boiler problem. Our plumber is stumped. Any ideas?

What was the design temperature of the system? 21C is the norm. If you don't know, ask the system designer/installer.

What is the outside temperature? Most systems are designed assuming it is -1C or -3C.

Which boiler do you have - make and exact model?

How do you know the system has been correctly balanced?

 

[AllyBongo]

Boiler make, model and size? How many rads? Boiler been commissioned properly?

 

[joni os]

Modulating. New super efficient boilers can recognise demand and adjust output accordingly. Previously humans brains did a similar but less complicated function by adjusting thermostatic control knob. As the brain of a boiler is zero the propensity to malfunction is now included by design.

 

[snowhead]

I don't know what you mean by boiler modulating.

Boiler stays on but the flame reduces so the heat output is lower

 

[Chalked]

Boiler stays on but the flame reduces so the heat output is lower

As its oil. I'm pretty sure modulating isn't an option! :chinese:

 

[joni os]

As its oil. I'm pretty sure modulating isn't an option! :chinese:

Sorry to say, even oil boilers have been infected.

 

[Chalked]

Sorry to say, even oil boilers have been infected.

I stand corrected.

Which ones? And how are they modulating a pressure jet?

Thanks ( sorry to hijack the thread)

 

[SimonG]

There's not many modulating oil boilers in the domestic market. Do the new blue flame ones modulate?

 

[joni os]

WB have a boiler that adjusts 12- 18 Kw. Literature says interactive. ie. does its own thing.

 

[SimonG]

WB have a boiler that adjusts 12- 18 Kw. Literature says interactive. ie. does its own thing.

Will have to have a look at that. Sounds like more sooty boilers when the system goes breasts up.

 

[SimonG]

To the OP. Has the boiler been commissioned and set up correctly? If it's not a modulating one then they run on a range of outputs. Different nozzles and settings will give you different outputs.

 

[Worcester]

Silly question... Do the radiators close to / in the same location as the room stats have TRV's on them?

 

[Worcester]

Aha !!!!

All radiators have TRVs.

 

[Nostrum]

Oil boilers don't modulate, you can only change the fixed output by changing nozzle sizes. Yes, they exist, but not in any great numbers here in the UK.

Even the blue flame technology is fixed output as far as I'm aware (Firebird have just launched one)

If the rads are at the right temperature and the room is cold, the rads are undersized or all the windows are open.

 

[Nostrum]

Actually, reading the post again; they may be sized accordingly, depending on what temperatures the rooms were designed for. Generally, 18 degrees is sufficient for bedrooms, 21 degrees for others. How hot do you find you need it to be to be comfortable?

25 degrees is pretty warm !

 

[Norcs]

Yes .. sounds like its working fine. The OP should invest in some wooly jumpers.
Modulating oil boilers. LoL.

 

[Wagger]

Thanks doitmyself. Answers. Will have to ask installer but when I said we wanted to get it up to 25c he didn't say that was not possible.
Temp outside been 5/8c not very cold.
Worcester Bosch Greenstar Danesmoor Ext 12/18
I saw the installer carry out the work when he came back to have a look at it but, of course, I don't know how well he did it.

 

[Wagger]

Greenstar Danesmoor ext 12/18.
9 rads - 1 v small.
Yes, has been commissioned separately

 

[Norcs]

he didn't say that was not possible

OOh dear. He shot himself in the foot there.
Was that before or after the installation was carried out?

Bigger rad needed probably.

 

[Wagger]

Yes they do but installer said that this was OK providing the TRVs were left o highest setting -5. What do you think?

 

[Wagger]

He said after

 

[Wagger]

Yes 18 in beds Ok but 21c not comfortable enough to sit in watching telly. We aimed at 25 to get system running full bore but can not get above 21, sometimes only 19. System seems to switch off when it reaches this level even though room stat hasn't reached 25. I would have expected it to keep belting away!

 

[Worcester]

See my previous posts..

Wagger you state that ALL radiators have TRV's

Were the stat is located there shouldn't be any TRV's the system is fighting itself.

Any well designed system should be able to get a house up to 25, especially with an outside temp of 5-8, for older people that are sedentary during the afternoon we ususally set their stats to 23 for the pm (we use programmable stats so can set multiple heating levels per day)

The system should have been designed for between -1°C and -3.8°C depending upon location.

 

[Norcs]

Fit a stove.

 

[lame plumber]

if all the rads have trvs, then the rad in the hall/room with the room stat will be fighting the trv for starters. Other option, buy some jumpers.................

 

[SimonG]

Did you get your certificate from building control?

 

[NRS]

Try removing TRV heads from rooms that are cold; sounds like trv's are shutting down before your desired room temp is reached. worth a try !!

 

[gmartine]

As lame said if TRV is in hall with stat, no boiler interlock.

Completely remove TRV head in the hall and see.

 

[Davide13]

Will a TRV open on 5 start to close then? Surely it will allow maximum flow all the time or are they calibrated to close even on max.

 

[Worcester]

Will a TRV open on 5 start to close then? Surely it will allow maximum flow all the time or are they calibrated to close even on max.

They'll close even on 5 and that could well be before the room achieved temperature because they are measuring the air temp immediately adjacent to the rad, not the room temp, hence a need even with TRVs for proper balancing

 

[Davide13]

Well that's something I wasn't aware of. I'll get me coat.

 

[Best]

In the OP it was said the radiators become hot, or very hot. So if that is true it has to be undersized radiators or a faulty wall stat (or stat fitted in wrong location above a radiator for example.)
Check the entire radiator surface is fairly evenly heated.
Give us an example of details of one of the rooms that isn't getting up to heat - radiator dimensions and if single, double extra, or double convector, plus size of room including height and how many outside walls etc.

 

[Wagger]

No. Plumber can self certify certain work and the boiler was commissioned independantly by an OFTEC approved commissioner.

 

[SimonG]

No. Plumber can self certify certain work and the boiler was commissioned independantly by an OFTEC approved commissioner.

Still would receive a buiding control certificate if it was kosher.

Boiler install is notifiable now. Not the commissioning. Fitted by one person and commissioned by another. There could be the reason you have issues.

 

[Wagger]

Room dimensions in metres 2.56 high x 5.0 x 4.2. 2 outside walls 2 double glazed windows total 2 sqare meteres. Radiator double panel with single convection 600 x 1200. Stat fitted in a suitable place.

 

[doitmyself]

They'll close even on 5 and that could well be before the room achieved temperature because they are measuring the air temp immediately adjacent to the rad, not the room temp, hence a need even with TRVs for proper balancing

Most TRVs have a proportional bandwidth of about 2C, so they are full open 1C below the required temperature and fully closed 1C above.

Not knowing what temperature 5 represents (it varies according to TRV make and model), it's impossible to say if it would interact with a room stat set to 25C.

 

[Best]

Room dimensions in metres 2.56 high x 5.0 x 4.2. 2 outside walls 2 double glazed windows total 2 sqare meteres. Radiator double panel with single convection 600 x 1200. Stat fitted in a suitable place.

I haven't worked out a rough output, but that is a fairly big room. I am sure I would have put a bigger rad in. Usually a double radiator for any room approaching that size, IMO.
Depends on what type of house and how good the insulation is. Also if a bedroom or a living room, as bedrooms require less heat output.

 

[Worcester]

21m2
Very old leaky house = 2.75kw
Brand new build < 840W

Average Flow temp 55° (condensing 60 F/50 R) looking for 30° delta T = 30° Radiator factor = 0.515

Therefore output from P+ 600*1200 = 1691 * 0.515 = 870 W

Therefore rad undersized unless new build.

 

[Worcester]

Problem Solved.

That's the difference, I guess your 'installer' isn't a heating engineer. They should have done full heat loss calcs first and sized the radiators (and boiler) accordingly.

Ask to see his calcs

 

[ShaunCorbs]

Problem Solved.

That's the difference, I guess your 'installer' isn't a heating engineer. They should have done full heat loss calcs first and sized the radiators (and boiler) accordingly.

Ask to see his calcs

+1 the only way I can get the existing rad working in a normal house is to have the room temp at 21 dc