Yes the rads are hot so boiler would seem ok. I only have one thermostat and that is in the hall. When it is mild, this clicks off when 20c/21c is reached. When it's cold it never clicks off as it never gets up to temperature. On the old boiler, I remember when elderly aunts used to be expected, we used to click it up to 23c and it reached that temperature. Mind you, it was very warm!
I've tested thermometer readings in each room - most are 18c, one is
20c. So it looks like draft proofing, but I come back to my original question, how can I get this tested? I'm reluctant to have cavity wall insulation if there's a chance that I end up with condensation when there might be little heat escaping anyway?
have a look at the original point and Ed's comment - i.e. are the radiators hot all over and is the return water temperature cool? This would be circulation issue. THe only other is if the boiler burn rate is set low as mentioned earlier. The fitter should be able to test that.
It's possible to work in two ways.
1) Calculate the heat loss. Measurements, materials and temperature drop. This is reasonably good. What you can't do is to reliably measure the heat required to heat the air replacing what's there - in other words, what is lost through draughts. There are typical estimates for that and these are taken into account when sizing a heating system - or should be. You could get a heating engineer to do this work for you but I am not sure that it leads anywhere.
2) If the heating were working properly and you know the temperature of the radiator on flow and return side, you can look up the output on a manufacturer's data sheet.
If 1) >> 2) then you have a problem that heat loss is greater than supply.
Two solutions to that:
a) Increase heat
b) Reduce heat loss
Draughts and loft insulation are probably the two first places to start. Cavity insulation and finally double glazing would follow in terms of return on investment.
However, I come back to the original point. It *was* working. Or are you perhaps not so sure now?
That happens if you seal up the house by going overboard on draught proofing and fitting double glazing and not having ventilation. Having cavity insulation may result in more window condensation because these now become the coldest surfaces. It can be resolved with having ventilation, avoiding release of too much water vapour (e.g. drying clothes on the radiator) or a dehumidifier.
Or there aren't enough radiators, or the insulatin is crap, or the doors are draughty..or anyone of a million things dismissed in your patronising and sweeping statement.
You ARE Drivel and I claim my free combi brochure.
On 23 Feb 2006 06:57:43 -0800 someone who may be "Ross" wrote this:-
To add to what the others have said, there will almost certainly have a local organisation that gives free advice on energy conservation, funded by the taxpayer.
A cavity is indeed there for a purpose, it stops damp from rainwater penetrating through the wall from the outside. Some of the original forms of cavity wall insulation did cause problems because they blocked the ventilation in the cavity. However, modern forms of insulation avoid this problem.
Internal condensation is due to poor ventilation of the rooms.
What should happen with your new boiler is as follows. Assuming that the building is cold then it should fire at maximum rate for some time, say one to three hours, to warm the place up. What happens next depends on the heating system and the boiler. With a room thermostat the boiler will go off until the thermostat calls for heat, which depends on the room. With just thermostatic valves the boiler will go on and off frequently, cycling. That is for a boiler with on/off control, a modern boiler may well modulate instead of going off, it turns down the output to a low level.
If the building was warm enough before then changing the boiler is unlikely to have affected the heating system enough to make the building suddenly cold. The problem is undoubtedly with the new boiler.
The message from Nigel Molesworth contains these words:
ISTM that in this case the more likely problem is the opposite - that the circulation is too slow. I wouldn't totally discount the notion that the flow rate is too high but that is easily checked by testing the flow and return temperatures at the boiler. As Andy pointed out earlier the design criterion is for a temperature drop in the region of 11C but the temperature drop would have to be much less for the boilers internal stat to induce frequent cycling.
Either way if the boiler is not firing continuously then it cannot be giving its maximum output. Given that the previous boiler at the same rating apparently performed adequately then the radiators should not be undersized which leaves flow rate to be investigated, sludging (and the characteristic cool patch) having apparently being ruled out.
So what are the flow and return temperatures at the boiler?
Gas fitter not withstanding boiler malfunction cannot be ruled out altogether but certain knowledge of the flow and return temperatures should be the key to solving the problem.
You seem to have missed an important point in the OP: "the old boiler was ok". My reply was posted before we were told it was the same size. Shame, I normally find your posts are well considered.
The boiler also has its own thermostat which controls the circulation water output temperature. The only thing thats changed is the boiler, so we know its the boiler. This is a classic picture of a boiler thermostat set lower than it was on the old one. We also know the trend is toward lower circulation temps than in years gone by etc. While I cant be 100% certain without checking the installation, this is surely the most likely explanation, and a new (boiler) thermostat that can go to a higher temp will resolve it.
The other way to resolve it, and imho a better one, is to fit cavity wall insulation. Fibreglasss and rockwool are ok re damp.
At first sight, it might seem that it does, because if there is a greater temperature drop across radiators the heat given up from them must be greater.
Unfortunately, it doesn't quite work like that.
Heat released is proportional to mass of water multiplied by the temperature fall. If the increased temperature drop is achieved by reducing the flow, then the energy output is not increased.
The only ways that heat output into a room can be increased are by having a larger radiator surface area or by running the system at a higher temperature so that the water to air temperature is increased. Increasing the system temperture to any extent isn't realistic in one already running at 82 degrees.
Turning down the pump has an equivalent effecet on the boiler. The heat exchanger will be able to raise the temperature of the water by so many degrees. On a conventional boiler, the design is around 12 degrees - hence 82 flow and 70 return.
This leaves only two possibilities for the problem if it was working.
1) The water flow has been reduced
2) The boiler is firing at a lower rate than its predecessor.
The reason that the boiler cycles is that either the thermostat is faulty or that the heat isn't being removed from it fast enough in comparison to its burn rate.
Given that we know that it *is* cycling, this only leaves faulty thermostat or low circulation.
Don't discount too high flow rate entirely. If the water can get back to the boiler sufficiently hot it will cause the boiler to cycle even though it is doing very little work.
There is another possibility that escaped me before. If the boiler in question has an automatic bypass valve that could be set wrongly and be passing hot water directly back into the boiler at all times.
I understand what you're saying Roger, but it would need a hell of a flow rate to achieve that if one considers that the original system will have been (should have been ?) designed for the standard flows and temperature drops.
That could be, or a manual bypass left open. A stuck diverter valve could also have an effect, although the DHW would then become very hot.
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