Bear with me a moment ... I'm shocked at the cost of running my small flat's combi boiler compared to my previous terraced house boiler which had a hot water tank. The cost has doubled (3bd house HW/CH with 4 occupants was £360pa over the year, 1 bd flat combi HW/CH with 1 occupant ran up £60 in December alone!) The flat is fairly modern (1982) in good condition, and I have the water/ch on from 6-9am and from 4-11pm, turning it off when CH gets too hot. Dec. is the worst month of the year measure usage, but even if it all drops 50% for the rest of the year, it's still too high for my liking.
The reason for posting here is that I have already asked about the inability of the boiler to provide a constant flow of hot water. (CH seems to be very hot whenever it's on whatever the thermostat on the boiler is set to).
Is it possible that the boiler has faulty thermostats and is failing to provide constant hot water, but also using way too much gas to feed the CH? Or am I just paying the price for having this kind of boiler? Is it possible that I'm using the combi boiler in the wrong way, and that these fixed timing settings are not appropriate to combis?
I plan to get a CORGI man in early in the new year to give it the once over, landlord or not!
Thanks, Jim
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You are not heating the water with the timer when using a combi. It may be you need thermostatic radiator valves and a room thermostat fitting to make the system much more efficient, especially with the comment you have to turn the boiler off when the CH gets too hot. The TRVs I fitted payed for themselves in no time.
Given that you currently have the heating on, and many months of the year you don't, I would expect to the difference between worst and best months to be closer to 90% (i.e. most hours of the day you won't be using any hot water and hence the boiler will be using no gas at all).
So a sample of costs taken from one month like this tell you nothing really.
That sounds like you do not have full thermostatic control in place (i.e. room stat, and thermostatic radiator valves on all rads (except the one in the room with the room stat).
What do you mean by failing to provide constant hot water exactly? (i.e. it works when the tap is first turned on, but the goes completely cold, or does it run warm but not as hot as when you started etc).
There are several issues here:
Firstly the thermostat for hot water in a combi just sets the upper limit on the temperature. i.e. if you are using hot water it should not supply it at a temperature exceeding that set on the stat.
The lower limit is usually set by the laws of physics. The boiler can provide heat at a rate governed by its basic design (tell us the make/model number and we can give you more info). The more powerful the boiler, the more water it can heat in a given time. Hence if you ask for a small flow of hot water it will supply it at a temperature governed by the HW stat. As you turn the tap on more, you reach the limit of the boilers power where even running flat out it can still not heat the water to the stat temperature and the temperature of the water will begin to fall. Select a high enough flow rate and it will not be able to heat it enough to get it to a usable temperature.
There is yet one more issue, that there can be times when you are asking for a small amount of hot water that the boiler is producing heat too fast such that it would end up exceeding the stat temperature an hence it has to turn off its burner. Some combis also use a relatively insensitive flow switch which requires a good flow of water to be requested before they will switch to hot water mode.
The moral of the story is that you need to choose your combi carefully since there are lots of crap combis on the market, with too little power, and lots of quirks when running. Alas if you landlord made the choice for you you can probably guess what end of the market he went for!
All things being equal with the boilers efficiency, there is no reason for a combi to be less efficient than a system boiler with a hot water cylinder. In fact it will tend to be more efficient since there is less risk of you loosing energy from the stored hot water.
Having said that, any boiler can be run inefficiently with poor (or no) control systems. You can also get a large variation in basic efficiency between different boilers (i.e. the worst will give perhaps 70p worth of heat for every pounds worth of gas, the best will give over 96p worth of heat).
Fair point - at least I *hope* I'm not. If I have the boiler set to HW only and switch it on, but with NO drain on the taps, the burner most DEFINITELY fires up.
won't be installing anything serious until I know how long I'll be here (at least a year, but could be a lot longer).
Jim
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Fair point, and if I optimistically assume the winter quarter as 50% of the annual bill, and assume December (with holidays) is 50% of the Winter quarter, I get an annual bill of £240 or £20pm which is much better, though my 3bd townhouse has an annual bill of £360 with 2-4 occupants!
I have this in another thread, but briefly if I try to run a bath (however slowly) the hot tap runs very hot for 30secs then drops from warm to cold in 5 minutes or so. At best I can only get half a bath of comfortably hot water.
I have the boiler thermostat on Low (out of L-M-H). I can here the thermostat click if I turn the dial up and down, but I still get steaming water for 30 seconds or so when I ri8unthe tap with the thermostat on Low. I tried running a bath with HW/CH running on High with no difference to the temperature of the flow.
This flat is a 1982 conversion and the boiler is almost certainly the original Worcester Heatslave 2+. I have checked it for CO and it's okay, my landlord's agent tells me it is checked annually.
I plan to turn the CH off and put the thermostat to High then try to run a bath. I think this would have happened in the autumn anyway (admittedly with the thermostat on low) and cold water after a few minutes still happened.
Thanks for all the other info which I've read and stored. I'll give a few tweaks a try, but unless I'm doing something very stupid (and I don't deny that's quite possible...) the CORGI man seems almost inevitable now!
Thanks again, Jim
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"JimGC" wrote | This flat is a 1982 conversion and the boiler is almost | certainly the original Worcester Heatslave 2+. I have | checked it for CO and it's okay, my landlord's agent tells | me it is checked annually.
The landlord's agent might tell you that, but by law they MUST give you a copy of the Landlord's Gas Safety Certificate.
CH OFF HW ON and thermostat to HIGH Burner can be heard inside the boiler.
I run the bath very slowly (quarter turn of the hot tap only) - 1 minute of very hot water gradually cooling until after a 5 minutes the water is coming out lukewarm. The burner can still be heard in the boiler, the radiators are cool (so CH *has* gone off)
Any ideas from this (other than to call the engineer, which I suspect is all I can do...!)
Thanks.
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Can you clarify exactly what you mean by you have the water/ch on? Are you perhaps using a two channel programmer in error as most combis have the HW permanently available regardless of the timer function for the central heating. In this case perhaps the installer wired up the two channel programmer so that ch is on even if the programmer thinks it is switching the hot water. Try to tell us what make and model of combi, what make and model of programmer etc you have installed.
CH on some combis is a fixed temperature the thermostat on the front is for hot water, however you could have two adjustable thermostats again it depends on the make and model of combi.
It's a Worcester Heatslave 2+ from 1982 (when these flats were converted, I believe). As it's a rented flat I won't be likely to have it replace but I'm sure I can persuade the landlord to have it fixed, if possible!
It has the following settings:
Programme:
----------- Off Constant Programme (timer with 1-on,2-off,3-on,4-off)
Temp:
------ High-Medium-Low
HW/CH selection:
---------------- HW All day/CH Off HW All day/CH Twice HW All day/CH All day HW Twice/CH off HW Twice/CH Twice HW Twice/CH All day
I usually have it on HW Twice/CH Twice.
For the test tonight, I ran a bath with it set to HW All Day/CH Off, with Temp set to High, and the programme to Constant. Same story: the burner is going like the clappers (heard, not seen) but after a couple of minutes max of very hot water it gets cooler until lukewarm after 5 minutes. Burner still going like clappers, but radiators have cooled down.
Given what I've read here it seems very strange that the burner is on (easy to hear it fire up) when only the HW is selected, and nothing is drawing on the water supply.
Hope this helps with some ideas! Thanks...
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Now I am a bit confused... the only "heatslave 2" models I could find are all conventional boilers and not combis. If yours is one of those then that would suggets that you have a hot water cylinder somewhere.
(A combi heats the mains cold water directly - there is no stored hor water).
Again witha combi this is normally a non issue. It has a CH mode and a HW one. When you turn on the hot tap the boiler goes to HW and stays there until you turn off the tap. Hence you get no heating when dawing hot water anyway.
Is this programmer built into the boiler or separate?
If it is built in, then I susspect were are not talking about a combi boiler here at all, since the concept of HW twice makes no sense. With a combi the HW should always be available.
Ah! Now I'm confused too - but that's why I wrote to the group! The only Heatslave boilers I could find on a websearch were described as combi - I also wrote to Worcester Bosch Technical support describing the problem have received the following reply:
"Thank you for your recent enquiry. Switch off the C/H demand and allow to cool, then with a demand for DHW check for power (230v AC) at terminal T4. If power present, it would indicate a possible fault with the DHW priority thermostat. If no power present, check the diverter valve for let by to C/H."
Didn't make a lot of sense to me, but he didn't contradict my description of the boiler as a combi.
The maintenance and installation instructions for this boiler (hidden in an old box!) doesn't explicitly say it's one or the other, but it only talks of a feed and expansion cistern with no indication of a water tank. In fact it talks more about flow rate regulation etc which I assume is related to combis - it gives an Optimum Flow rate through the heat exchanger of 3gpm (whatever that is!)
I think it is a combi, (specifically, the Worcester Heatslave 2+ G50 Deluxe) though I'm happy to be proved wrong if it's not. I suspect my next move is to get a CORGI engineer in to do the above checks and give the thing a once over - not just for safety but for operating efficiency. I wonder whether this is my responsibility or the landlord?
Ah well, thanks - any more suggestions or help will be very welcome!
Jim
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If the Worcester Heatslave is the machine I'm thinking of it does indeed have a CH + HW programmer, and it is a combi.
Some combis come on from time to time to keep the water in the heat exchanger hot so you have really instantaneous hot water when you turn on a hot tap, so I guess this boiler uses the HW programmer setting to determine when to do this. If the diverter valve is on the blink it might just explain why it carries on heating up for 10 minutes, and also whey you only get lukewarm water after the initial spurt of scalding hot water.
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