Confused by Thermostat

[footprints]

No point in tampering with the stat position or setting then.
Even if you have the balance way out some of the rooms would be baking hot.
It make me wonder if the boiler is big enough or set correctly for the size of house, assuming the insulation is reasonable, eg; D Glazing and loft insulation.
It really needs a Gas safe engineer to check the gas rate / pressure and give an opinion on the boiler size, which is not a DIY job as you can imagine.

Unless I have missed it you don't say how old the boiler is.
If it is an old boiler it might even have been installed for partial heating very common in the 60's just rads downstairs, then people add more rads or extensions.

 

[Groover75]

Update - the boiler has been on continually from 5am to 10pm yesterday and from 5pm until now (1:30pm) today.

The thermostat in the hall now reads 19.5C, so it has crept up 0.5C over the last 24 hours. It's target temperature since yesterday has been 22C.

However - the temperature in my home office upstairs has risen from 19.5C yesterday to 23C today!

So the hall can''t really increase in temperature and can't get to the target, but the rooms are heating up OK. The hall radiator is one of the two hottest in the house.

What conclusion should I draw from that result?

I think the boiler is only a couple of years old as the previous owners left an invoice for electrical work.

Thanks, Andy

 

[Groover75]

Duplicate posting - deleted

 

[gigz]

Whats the model of the boiler and what have you got the boiler stat set at ?

 

[Groover75]

Worcester Greenstar 40CDi Conventional, installed August 2011.

The temperature control on the boiler is set at 6. Then there is a dotted line and you have to press hard to take it higher.

Andy

 

[D_Hailsham]

Worcester Greenstar 40CDi Conventional, installed August 2011.

How large is the house and how many radiators?

 

[Groover75]

13 radiators. Five bedrooms, three reception rooms. I have the radiators in three bedrooms and one reception room turned off.

Andy

 

[D_Hailsham]

13 radiators. Five bedrooms, three reception rooms. I have the radiators in three bedrooms and one reception room turned off.

So that's 17 rads in total?

Assuming 1.5kW per rad, that's 25.5 kW. Add say 3.5kW for heating the HW cylinder you get 29kW.

I wonder who decided that a 42kW boiler was required???

As a check, use the Whole House Boiler Size Calculator. This suggests 2kw for the cylinder, but can be changed.

 

[Groover75]

Sorry, it's 13 rads in total, with four of those currently turned off.

So it seems safe to say that the boiler is large enough for the house. Right now I can heat the house up better with the coal fireplace.

I have a gas safe person coming out on Monday.

Andy

 

[D_Hailsham]

Sorry, it's 13 rads in total, with four of those currently turned off.

So it seems safe to say that the boiler is large enough for the house.

NO.

The problem is that the boiler is much too large for the house and the number of radiators you have.

If you have only 9 rads working - that's about 13.5kW, they are being given the impossible job of extracting heat from a boiler which is three times the size. The boiler will try to modulate down to provide the required heat (min approx 10kW) but I suspect it is not capable of doing this fast enough. The net result is that the return temperature rises faster than the system anticipates and, as a consequence, the flow temp rises very quickly, exceeding the set temperature, and the boiler cuts off until the water has cooled down. The net result is that the average flow temperature is lower, so the rads do not give off enough heat.

You can check if my theory is right by monitoring the boiler when the system is heating up from cold. If it's continually turning on and off, you will know why.

It is possible to restrict the max output of your boiler (the engineer should know how), so it might be worth experimenting by setting it to about 21kW.

Have you done the Whole House Calculation?

 

[Groover75]

Thanks - this is more complex than I realized.

The whole house calculation gave 28.68 kW.

I will report back what the gas safe person tells me on Monday. Thanks for the help!

Andy

 

[D_Hailsham]

The whole house calculation gave 28.68 kW.

That sounds a lot, even for a five bed house. Can you post all the data you entered into the calculator?

If it is correct, the average size of your 13 rads should be over 2kW.

Check your rads using the Stelrad Catalogue, page 50 (Elite 50 Δt).

 

[Groover75]

Bolder was serviced. Service person tells me that the boiler is the right size and everything is working fine.

The temperature dial on the boiler goes from 1 to 6 and then after 6 there is a dashed line to "max". He told me that I need to have it on max all the time because it is a large house. The difference between 6 and max is about 30C in water temp.

I almost got into an argument with him about the thermostat. I think we were misunderstanding each other.

I'm beginning to think the problem is this: the t/stat is in the hallway and my hallway is massive. Larger than any other room in the house. It has a single average-sized radiator to heat all that space. This radiator is belting out heat with the boiler on "max", but perhaps it just isn't enough. Also it seems silly to be heating such a large space that isn't lived in.

Andy

 

[jackthom]

Assuming the hall thermostat is responding correctly to changes in temp ( a cheap thermometer hung close to it would be a useful check) why not set it so the hall is around 18C. This will probably mean the rest of the house will be more than comfortably warm and the boiler might actually switch off a few times during the day, saving a bit of expensive gas.

Other alternatives include moving the thermostat to a suitable living room (portable RF units are available) or fitting a much larger double radiator in the hallway.

 

[Groover75]

Hi Jack,

The problem seems to me that the hall is currently the warmest room in the house, when I want it to be the coldest.

Andy