It's a stupid central heating question!

[steve]

I've just moved into a 6 month old flat - two bathrooms heated by towel radiators and two bedrooms, a living room and a hallway heated by Terrier II radiators. The boiler is an Ideal Isar HE30.

It's been a pretty cold day today, I think outside's only got as far as 2 above freezing and it's currently about 2 below so I'm guessing a heating system's gotta work pretty hard against what's going on outside.

However...

I got up this morning and put the heating on as it was about 19 degrees in the living room and I like it to be nearer 24. Fourteen hours continuous use later and the place is still only 22 degrees, and that's with running the cooker hob for about four hours to warm up the kitchen/living room. I tried turning the hob off for a while but the temperature started dropping...

So, I know nothing about boilers, radiators or DIY in general so I'm not going to ask you qualified folk for suggestions as I wouldn't be able to answer any technical questions so in a word, yes or no, it sounds screwed doesn't it?!

[EricP]

You have a boiler with decent specs

Ideal Isar HE30 Condensing Combi Fan Flued Condensing Combi Boiler.

8.8 - 29.3 kW 30 - 100k Btu's

12L per min @ 35 degrees centigrade

For a flat you should be roasting.

[steve]

You'd hope wouldn't you?!

I'm no heating expert but fourteen hours seems like a long time to reach 'a bit chilly'.

[Andy Hall]

The design convention is that a heating system ought to be able to maintain the temperature of a living room at 21 degrees when the outside temperature is -3 degrees.

Heat loss, which is effectively what the heating system compensates for, is proportional to the temperature difference between the two places. In other words, the heating system should be sufficient to maintain a temperature difference of 24 degrees.

Given the 2 degree outside temperature and needing to supplement the heating with the hob, something is clearly wrong.

Either the installer didn't calculate the heat loss properly and installed inadequately specified radiators, or he didn't bother to balance the system properly and insufficient water is flowing through the radiators.

Given the size of the boiler, it is unlikely in a flat that it has insufficient output.

You could try measuring the temperatures at each radiator valve, or feel the cooler end. If it is notably cool, then try taking off the lockshield valve cover and opening the valve some more if you can.

If the radiator really is getting hot throughout, then it may be undersized. You could do the calculations to check that, or given that it's a new place, get the building firm to address it for you.

[Sparks]

How hot are the rads getting, are we talking too hot to touch, or just a bit warm? Do you have a thermostat somewhere mounted on the wall, what is this set to if so? There is a pressure gauge underneath on the right side, what is it showing? What is the knob on the far right set to? There is an LED display that should be displaying 0 - is it?

Now, not meaning to be patronising, but you haven't got all your windows open have you ;-)

Sparks...

[Dave Liquorice]

Have you found and adjusted a room thermostat anywhere or simple switched something to "on"?

Personally the only thing that sounds screwed to me is an interior temperature requirement of 24C. 19C is comfortable in a T shirt, drop it to 18 or 17 and a jumper is required.

[Set Square]

The boiler is certainly plenty powerful enough for the job - so either something isn't working quite right, or the rest of the system may not have been designed adequately in terms of radiator size.

When the flat wasn't as hot as you would like, how hot were the radiators?

There should be a pressure gauge on or near the boiler. What pressure does it show when the heating is on?

Is the flat literally 6 months old - i.e. built from scratch 6 months ago, and presumably built to current insulation standards - or was it created by converting an existing building into flats?

[Roger]

The message from "steve" contains these words:

You don't give us much to go on but modern buildings should be well insulated and the heating control system have more to it than an on off switch so a few random observations in no particular order.

1 Have you got a room thermostat set to less than 22 degrees or thermostatic valves on each radiator set to less than maximum? 2 Is the boiler heat control turned up to maximum?

3 Do all the radiators get anywhere near hot. If any of the radiators have a cooler section at the top it means they have air in them and need bleeding.

1. After a cold night how come the temperature was at 19 before you switched the heating on?

[steve]

They're getting pretty hot but I can put my hands on them without needing a hospital... Back at the house I've just moved from, the radiators were too hot to touch.

It's a Danfoss TP5 in the hallway which is set to 19 overnight which I increased to 24 when I got up. It pings and the boiler fires up and everything gets going, but it's never warm enough. I set it to 20 last night and it was around about that temperature when I got up this morning. I increased it to 22 and it rose pretty quickly 'til I turned the oven off - since then it's been pretty stable at about 22 but it's just started to fall again.

The black scale is just over 2, the red around 30. It doesn't actually tell me what the scale *is* but the needle's pretty much half way.

Ooh, I made sure *that* was maximum!

It says 'c' when it's heating and '0' when it's reached it's temperature. So for 16 hours yesterday it was reading'c'... I've just done a timing and the burner comes on for 36 seconds then goes of for 4 minutes while the pump keeps running. Seems pretty sparing but I guess that's right.

Hey, do you think closing them would make a difference..?!

[mike ring]

"Dave Liquorice" wrote in news: [e-mail]:

I've got to agree - I'm a chilly morsel, at work I had a fan heater under the desk to provide my own microclimate.

But 24 is way too hot for me

mike

[Andy Hall]

This probably implies that the temperature is around 60 degrees or less. You can touch for a very few seconds but that's about it.

The conventional design with traditional boilers is to have a flow temperature of 82 degrees and return of around 70 degrees.

With newer boilers of condensing type, the burner can modulate down and also they are suitable for running at lower temperatures. Thus, it is possible for radiators to be sized for that and the whole lot to run more efficiently (condensing boilers are more efficient at lower temperatures).

However, in this case, it seems unlikely that this was done because the heating is inadequate.

There are a few things to try:

- Check the CH thermostat on the boiler. Turn it all the way up if it is not already there.

- Flow through radiators is inadequate. Check the lockshield valves on the radiators. Open the one(s) for the living room radiator(s) to fully open. Are the radiators in other rooms hotter? If so, turn the valves of those down a bit.

- Is there air in the radiators? They will feel cooler at the top. Bleed them if so.

OK, so the system can maintain 19-20 degrees relative to outside but that's about it.

This is the system pressure in Bar. Around 2bar is OK.

Answered that one.

This is a problem and indicates that the water flow through the system is too low. Refer to valve setting point above

It is also possible that the system wasn't flushed properly on installation and there is a partial block of the flow.

Definitely.....

[John Rumm]

Aha...

The ISAR is a modulating boiler that can cover quite a large range of power outputs. The fact that yours is cycling would suggest that your boiler is sensing a heating load far below its minimum modulation threshold. The nett result is that in spite of being capable of providing heating at say 24kW, it is only actually doing it at (probably) less than 3kW. This would explain you long heat up times for the house.

So it brings us back to a few possibilities: either the balancing of the heating is very wrong, or the radiators are way undersized, or possibly there is some silly in the pipework.

A balancing problem is likely (given we are talking about a newish property that would probably have been built with a reasonable level of insulation). It may be there is one rad that is taking the bulk of the flow and hence allowing most of the water to return to the boiler at almost the same temperature that it left it. The boiler would interpret this as the house being up to temperature with most TRVs shut down. Hence it throttles back its output to match.

Similar to above would be a pipework funny. Perhaps someone has installed a bypass on the boiler that is opening with too little flow resistance - again having the effect of short circuiting the water flow and fooling the boilers control system to modulate right down. Could even be something really dumb like a bridge directly between flow and return pipes.

The last problem (undersized rads) is harder to fix since you will need to change some rads. It might be worth looking at what sizes you currently have and if they are single or double panel. That will give a good indication of if this is the likely problem, or if it is more likely to be one of the above (or something else I have not thought of! ;-)

[Dave Liquorice]

People get accustomed to enviromental. Anything above the low twenties for me is getting too hot, I don't think it's "cold" outside until it gets down to below 5C (assuming there is little wind so not much wind chill). We have to remember to light the fire and crank up the heating if low landers or even worse southerners come to visit...

[<me9]

My house is well insulated. I sized my radiators on this basis. They will mainatain the temperature difference the system was designed for, but take an age to get up to temperature. Should I have allowed a larger factor* for intermittent operation than used to be applied with less well insulated systems?

• I /think/ I used a factor of 1.2, It was 10 years ago. I don't think we have had any sustained cold weather since (until now!).

[<me9]

I'd agree, but SWMBO certainly doesn't!

[Ian Stirling]

Yes, probably.

If the radiators can in each cases make up the entire heat loss, the rate of heating is dependant on the left-over power. If you've gone from a badly insulated house, with 20% over, to a well insulated one with 20% over, and the same mass of 'stuff' (chairs, internal walls, ...) to heat, then you may have half the power available for this that the poorly insulated house does.

[Set Square]

I'm not so sure. This may be true in absolute terms - if the house has been unheated for weeks, and you are starting from scratch. But with a regular daily heating routine, a well insulated house will cool down a lot less when the heating is off than will a poorly insulated one. So, although the *rate* of temperature rise may be less, the *time* to get warm shouldn't be a lot different.

[Ian Stirling]

Maybe. For example, my poorly insulated house has a quite large thermal mass in the heated sand below the floor. Insulating this properly will substantially decrease the thermal mass.

[steve]

What can I say, I'm a bit of a girl!

[Ian]

"You have a boiler with decent specs

Ideal Isar HE30 Condensing Combi Fan Flued Condensing Combi Boiler."

The specs may be good but the performance is not, in my experience. had an IDEAL ISAR INSTALLED GETTING ON FOR FOUR YEARS AGO AND I WISH HADN'T. In a special deal, we got two years of free warranty -- and bo did we need it. We've had so many different engineers out and so man different PCBs: the boiler kept banging (fixed), went through th lexicon of fault codes (DHW temperature sensor, return temperatur sensor, flame detection, etc etc). This was blamed on all manner o things, including a faulty electrical supply to the socket the boile was plugged into, which we got checked out by a sparks and which prove untrue. In the end Ideal sent their chief engineer down from Hull t pull the thing apart and managed to sort it out. Once bitten, twice shy, we took out Ideal's own service contarct onc it was out of warranty, and it has proved very useful. yet despite th leaflet supplied with the warranty claiming "We'll have an enginee targeted to be with you the next day", the most recent breakdown (L "Flame detection", claims the service booklet, and we know our ga pressure is fine because we had that checked too thanks to a friendl Corgi-reg neighbour who won't touch the boiler so as not to invalidat the insurance deal) was yesterday, a Friday, yet they're only offerin us an engineer for the following Thursday. Despite our protests. That' six days without hot water or heating in December. Thanks a lot. My advice is, don't buy an Ideal Isar. At times it has seemed 50-50 a to whether it has worked or not. Our experience has been a nightmare.

EricP Wrote:

-- Ian