HI, I don't know if this is a problem but I thought I would ask some advice. We have a Worcester boiler connected to a Megaflow pressurised system. The water return for the radiators and hot water are connected to 2 separate flow valves and then after the flow valves the pipe joins to enter the boiler. We have a sunvic electronic thermostat that controls whether the boiler starts - we want to replace this with a honeywell evohome if possible. I noticed that when I put the temperature down on the thermostat, the heating stops and doesn't come on- so this is working fine no problems. However, when I put the temperature right up, the boiler does start running but it runs for about 30 seconds then stops for 20 seconds then runs again. It does this continuously. The radiators get hot OK. I just wondered if the boiler is meant to work in a pulsing manner rather than continuously? Maybe it is a way to be economical with gas?? Thanks in advance.
Hi Luke the symptoms you are describing is called short cycling and is not an efficient way for your boiler to be working. This is mostly due to either a failing pump or oversized boiler but will depend on the age of the boiler. All new gas boilers will modulate themselves down to meet the demand of the heating load. It is normal for the boiler to come on and off but not at the rate you described. is it a sytem boiler or heat only? model of boiler? is there a auto bypass fitted? how long does the system take to heat up? Regards Dan
Thank you. Just re-read my initial post and it was slightly wrong- the zone valves are on the flow from the boiler not to the boiler. The boiler doesnt short cycle when it is warming up from a cold start- it only does this when the system is at temperature- the power dial is set to maximum so wasnt sure whether it was just putting a little extra heat in to keep it ticking over. Not sure what other boilers so when they get to temperature. The boiler is a condensing type 28cdi worcester about 10 years old but it has been rebuilt over the years with new parts- yearly serviced by worcester and they have replaced the pump, expansion container, pipework etc etc. It is a boiler that provides heat and water heating in a Telford tank. It takes about an 1- 1.5 hours to heat up as quite a bog victorian house. Not sure if I have an auto bypass...
In theory the boiler should be able to modulate down to cope with the much reduced demand from the warmed house, but perhaps it's because it's set at 'max' output; it fires up to max, cannot get rid of the excess hot water fast enough (the 'return' will also be warm at this point), so shuts down ('overheat' sensor) until the return water is cooler? You could try turning the output down a tweak and see what - if any - difference that makes (if it's at '5', turn it to '4'). Bear in mind, tho', that your large house may well need it to be set at max output during this cold spell. But, worth a trial chust to see? Regardless, when the weather does become more mild ootside, you should turn your boiler's output down a tad to match. Basically, the cooler your boiler runs the more efficient it will be - provided it's still running hot enough to get your house up to temp in the same reasonable time (ie - don't turn the boiler down so much it's running all the time but never trips the room 'stat!)
Thanks again- yes I think you are right about this- if I turn down when it is hot enough then the boiler goes longer in between firing up. The problem is, as you correctly state, that not having at max when cold means the radiators are not quite hot enough. We never really know what level the boiler dial should be at - I guess max for cold, medium for less cold etc...
That's pretty much it. The output control adjusts the output temp - that's it. And, yes, if you can lower it a tad when it becomes milder, you'll probably make a (slight...) saving. More advanced combis can have a weather compensator added, which is like a room 'stat except it sits outside. This tells the boiler how cold it is ootside and the boiler adjusts its output accordingly. It's all in the aim of keeping the output temp as low as possible, so that the return temp is ditto. And it's the return temp which causes most of the condensing inside the boiler, improving its efficiency.
CAN ANYONE HELP......... We have a Worcester Combi boiler and I changed the gas bottle yesterday and ever since although it started up alright at first, it keeps coming up with no ignition flame error code. I ave been through the instruction manual a million times and tried the tests and air purge and cannot work out why this has happened. It is driving me insane! Please does anyone have a simply answer for me, it's freezing here with no hot water or heating. I've tried resetting several times and it fires up but then cuts out each time. yours in hope!.......
Hi Lizzie. I've no idea. BUT - please start a new thread where you will likely get more attention from the pros.
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