Combi boiler cycling

meat_n2_reg

Hello 
Have recently has new Worcester Bosch 4000 combi boiler installed along with 9 radiators and looking at Hive to see how boiler usage is going 
Hive thermostat ( in lounge) is set to 18c ( 2 rads in lounge TRV set to 4 ) , Kitchen TRV set to 3
rest of radiators set to 2 or 3 
Boiler seems to cycle approx 2 times an hour once up to temperature , flow set to 65c 
Does this seem right ?
thanks Steve 

Lorian

How long are the cycles.
How long does it take to warm up in the mornings?
What is the return temperature?
Have you tried a 60c flow to increase boiler efficiency?

meat_n2_reg

Looks like  cycles are approx 5 mins
Rads take approx 20 mins to get fully hot and about 45 mins to get house up to wanted temperature
Don't know return temperature
Tried 60c but seemed to increase heat up too much
Today has ran for approx 4 hours but only used approx 20 kw gas so about £1.40 from meter readings 
Regards Steve 

Veteransaver

Twice an hour seems ok. It's not really cycling though it's just topping up the temperature as it falls. It's pretty nippy out so you'd expect it to come on and off at regular intervals. All depends on outside temperature and heat loss / level of insulation.
If the graph of temp in the hive app seems fairly stable it should be fine. Hive does "learn" so can often overshoot at first. But Eg if temp was set to 18 then it may shut off at 17.6 or something whilst the room continues to warm. It will learn the heating characteristics, but I don't know if it also looks at outside temperature, some do I think.
Cycling is really an issue if it keeps firing up  every 5/10 minutes or so. Modern gas boilers have a default setting often at 20 minutes. That default setting can be a problem though getting the house up to temperature if either the pump speed isnt high enough or your system is sludged up, as the boiler simply can't get rid of the heat quick enough, so it hits it's max temperature, then shuts off for 20 minutes meaning the house takes ages to warm up.
For modern condensing boilers to operate at max efficiency ideally you want a nice decent flow and a cool return temperature. So running the boiler temperature at the lowest temp you can get away with is the most efficient, but unless it has weather compensation (where it changes the flow temperature depending on outside temps and learns the heat characteristics of your house and system) you'd have to do it manually.
Hive doesn't do this though as far as I can see so you'd need to manually change the flow temps.
Don't forget on a combi there is a DHW flow temp, and a system flow temp, they are different settings.
Usually you'd want the DHW at around 50-60, but the system flow temp you'd want anywhere between about 35 and 75 depending on the weather, insulation levels and size of your radiators.
Eg a well insulated house with big rads and underfloor might get away with 35C flow temp or even lower, an old draughty house with single panel rads might need 75C to get warm and stay warm in cold conditions 

meat_n2_reg

Many thanks for all your help , will try reducing flow to 60c , house is 3 bed semi from 1970s so not the most energy efficient
Have new double glazing and loft insulation but no cavity wall insulation yet 

Graph in hive is stable and hot water is 50c

Regards Steve 

Reed_Richards

I've had a quick look online and it seems that neither your boiler nor your Hive support Opentherm wiring.  Therefore Hive cannot turn down your boiler output as the thermostat reaches the set temperature so your boiler is more likely to cycle.  The boiler will still modulate down as the return water temperature increases but it won't be as well controlled as in Opentherm.  

meat_n2_reg

Thanks that's a shame guess Worcester Bosch lock communication protocols?

FreeBear

Veteransaver said: For modern condensing boilers to operate at max efficiency ideally you want a nice decent flow and a cool return temperature. So running the boiler temperature at the lowest temp you can get away with is the most efficient, but unless it has weather compensation (where it changes the flow temperature depending on outside temps and learns the heat characteristics of your house and system) you'd have to do it manually.
Hive doesn't do this though as far as I can see so you'd need to manually change the flow temps.
Don't forget on a combi there is a DHW flow temp, and a system flow temp, they are different settings.
Usually you'd want the DHW at around 50-60, but the system flow temp you'd want anywhere between about 35 and 75 depending on the weather, insulation levels and size of your radiators.
Eg a well insulated house with big rads and underfloor might get away with 35C flow temp or even lower, an old draughty house with single panel rads might need 75C to get warm and stay warm in cold conditions

Had a new boiler fitted during the summer (a Viessmann 050 30KW combi). A late 1920s semi with a decent amount of insulation in the loft and new double glazing all round. Currently running with a flow temperature of around 50°C and DHW at 45-50°C.

Around 3°C outside overnight, and the heating kicked in for about 17 minutes at 2 hour intervals just to maintain a base temperature of 17.5°C. Fired up at 07:00 for 1h55m to lift the temperature to 19.5°C and have used just 20KWh today - Stove in the lounge was lit around lunch time, and is keeping the house nice & warm.

I can get away with running at a low flow temperature of 50°C as most of my radiators are some 30% larger than a basic heat loss calculator suggests. I use the Stelrad one, but compared to other online calculators, it does seem to recommend overrated sizes by default. Not a bad thing..

markin

You could set it to 50c and set it on 1.5 - 2hrs earlier than wanted and in it should not use more, If it runs more efficiently it should use less gas, Outside temps have to be the same or accounted for to get a clear picture of gas use at 50c vs 60c.

What most people do is mark the dial or take a note of the flow temp needed for 10c, 0c or -10c outside temps.

meat_n2_reg

Changed flow temperature to 60c took alot longer to reach target temperature , at 65c flow takes approx 45 mins and at 60c took over an hour 
Going to try flow of 70c for comparison, not sure if that's too high for condensing mode ?
I am recording gas usage for each setting
For reference heating is on for 1.5 hrs morning and evening so only 3hrs a day , so maybe a 70c flow might work better?

Alnat1

You could go with the 60C and set the heating to come on and go off half an hour earlier. 70C is likely to be too hot for condensing.