Have installed 927 stat it looks great but it takes for ever for house to heat up. New powerful boiler grant vortex oil 26-36kw. stat is set to oil boiler as recommended by Honeywell and optimisation is enabled but it is not bringing the boiler on enough to heat house. Stat is in hall where the rad has a manual valve fully open all other rooms have TRVs. WE have 11 radiators bot only 4-5 are on at any one time. Heating comes on at 4.30 afternoon target temperature is 19 deg. It is between 8-9 pm before it reaches this from a starting temperature of 16 deg. Would be grateful for any advice. Setting on boiler is 70 deg and I was told by Grant Technical people not to put the boiler to full. Although I read in various reports that boiler should be on full when controlled by a room stat. This is a new boiler £1200 condensing I can only assume the makers know what they are talking about and I am worried that I may have problems with warranty validation. . In the Honeywell literature no mention is made that I can see about what temperature boiler should be set at. But surely the CM927 should be bringing on boiler more often to reach target temperature. In literature it mentions that the boiler cycles 3 times per hour - each cycle 4 mins. I am baffled.
Honeywell cm927 very slow to heat house
- Thread starter liam2308
- Start date
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First of all the Honeywell CM927 doesn't heat the property. It's a room thermostat. All it does is switch the system off completely when the set temperature is reached in the room it is located. And that's it. It has no other control of the boiler.
Boilers are there to provide a supply of hot water to the heating system at a temperature you select using the thermostat on the boiler.
With condensing boilers when the water returning to the boiler is cooler this can improve the efficiency, so a lower boiler thermostat setting is often recomended.
Often the boiler gets the blame when really the reason the property is cold is because the radiators are too small for the property, or are full of sludge, the pipe system is badly designed, the poor thermal properties of the building or lack of insulation.
Is the water flow pipe leaving your boiler hot? if so the boiler is doing is job. You can check that it's working OK by getting a cheap strap on thermostat from a DIY store, clipping it to the boiler flow pipe and checking that the correct temperature is reached and maintained.
If that's OK and the property is not getting warm, then you need to look at the rest of the system.
Boilers will normally fire continually for a few minutes when first switched on, then as they get up and running, cycle on and off or modulate depending on the type to maintain the set temperature of the water leaving the boiler (usually 60-75 degrees C), If they ran permanently on maximum the water would boil. The less radiators you have on, the less heat is emitted into the property and so, the less the boiler operates to reheat the water when it gets back to the boiler. This is all controlled by the boiler, not the room thermostat.
It could be that the house isn't warm because you only have half the radiators on! heat from the heated rooms will leak into the unheated rooms.
Boilers are there to provide a supply of hot water to the heating system at a temperature you select using the thermostat on the boiler.
With condensing boilers when the water returning to the boiler is cooler this can improve the efficiency, so a lower boiler thermostat setting is often recomended.
Often the boiler gets the blame when really the reason the property is cold is because the radiators are too small for the property, or are full of sludge, the pipe system is badly designed, the poor thermal properties of the building or lack of insulation.
Is the water flow pipe leaving your boiler hot? if so the boiler is doing is job. You can check that it's working OK by getting a cheap strap on thermostat from a DIY store, clipping it to the boiler flow pipe and checking that the correct temperature is reached and maintained.
If that's OK and the property is not getting warm, then you need to look at the rest of the system.
Boilers will normally fire continually for a few minutes when first switched on, then as they get up and running, cycle on and off or modulate depending on the type to maintain the set temperature of the water leaving the boiler (usually 60-75 degrees C), If they ran permanently on maximum the water would boil. The less radiators you have on, the less heat is emitted into the property and so, the less the boiler operates to reheat the water when it gets back to the boiler. This is all controlled by the boiler, not the room thermostat.
It could be that the house isn't warm because you only have half the radiators on! heat from the heated rooms will leak into the unheated rooms.
Many Thanks Stem - At last I am beginning to see some light. No problem with the boiler - the outflow is very hot. New radiators in hall and living room. Sludge etc is not an issue. They get hot. I was under the impression that a room stat called/controlled the boiler until the target temperature is reached and then held it there for the time period required. Knocking it on and off. From what you are saying the boiler does its own thing and when the stat is satisfied it knocks boiler off. I honestly thought that this room stat would control boiler by bringing it on intially obviously within the boiler controls (cycle times so that water is not boiling) But with this stat calling for heat - green light on receiver boiler is only comming on for 12-15 mins in the hour is this normal especially when heating up initially. The technical people at Grant told me this boiler would heat this house no problem on minimum setting!! House is 1500 sq.ft.Double glazed -270 mm insulation. Boiler 26-36kw. From what you are saying I have just to turn heat up on boiler. Point taken about heat leaking into unheated rooms. I am very careful about closing doors in these rooms. There is only 2 adults in house. Again many thanks I have surely got the wrong impression on what a room stat does.
When the house is heating up and the room temperature is below the thermostat’s proportional band, the thermostat heat demand (flame symbol) should be on constantly. The proportional band is a range of temperature (default 1.5C) around the set temperature within which the thermostat reduces the heating output by switching the heat demand on and off in accordance with the time proportional output settings (cycle rate, minimum on time) to a point where it achieves and then maintains the set temperature. So with a set temperature of 19C, your radiators should be at maximum heat (as set by the boiler temp) up to around 18.5C. You should then find that the average radiator temperature drops once the set temperature has been achieved.
If the house is much slower to heat up than with your old set-up, then it does sound like there is something wrong.
If the house is much slower to heat up than with your old set-up, then it does sound like there is something wrong.
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Spot on. Sorry I used quite so many words to say that.
Again many thanks - now starting to get an insight how this stat is working. Cycle rate is 3 per hour and min. on time 4 mins as recommended by Honeywell for an oil burner in their category 2 settings. Proportional band is now making sense. Last night I increased stat to 20 DEG. Starting at 4.30 from 16 it got to 19.5 around 10.00. At about 6.00 it was 18.5 but as you mention this would satisfy stat. sometimes the flame signal was on and sometimes of. But because of the band of 1.5 either way I presume. Stat is satified. So from 18.5 to 20 stat is happy and at 20 would be knocking of boiler to cool radiators. So I would say that it it is working fine and should give me a more controlled temperature and hopefully be more economical. many thanks to both Mikely and Stem.
The Honeywell CM has a very generous optimser programme, so I doublt that the CM is causing the problem, have you checked the flow & return temperatures with an acurate digital thermometer, Grant VTX's have their boiler thermostats limited to 70'c, but we have been to a few where they have not been acurately set, so it would be worth checking, if the temperature is low, remove the thermostat dial, you will see a wire pin which can be rotated around the back of the dial, move the pin round another notch, keep doing this untill you get 70'c on the flow, you should be getting around 55'c on the return 
how long av honeywell been fiting burners in there stats
The Honeywell CM has a very generous optimser programme, so I doublt that the CM is causing the problem, have you checked the flow & return temperatures with an acurate digital thermometer, Grant VTX's have their boiler thermostats limited to 70'c, but we have been to a few where they have not been acurately set, so it would be worth checking, if the temperature is low, remove the thermostat dial, you will see a wire pin which can be rotated around the back of the dial, move the pin round another notch, keep doing this untill you get 70'c on the flow, you should be getting around 55'c on the return
This is a new boilerhouse model - I have it in the garage. On the dial there are no numbers just a graduated black marker - thin going to broad. At present I have it about 2/3 rds of the way up. I will try and get my hands on a digital thermometer but you certainly could not hold your hand on the out flow pipe - it is very hot. Many thanks for your information - I would prefer not to fiddle with dial until I check temperature with thermometer.
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