boiler cycling

[mpooley]

I have a 2 year old Grant vortex 35 (i think)
which seems to come on and off a lot.
I have just been timing it at exactly 1.5 mins on and 1.5 min on.

The house is up to temperature at the moment I don't know what it does when the house is cold.

I just wondered if you think this is normal or if this is cycling too much.

The stat on the boiler is turned to max ( It can go up more but only if a plumber changed the jet )

any advice would be appreciated

Mike

 

[D_Hailsham]

I have just been timing it at exactly 1.5 mins on and 1.5 min on.

What type of room thermostat do you have?

 

[mpooley]

I have just been timing it at exactly 1.5 mins on and 1.5 min on.

What type of room thermostat do you have?

It is a Danfoss TP500
oh and the boiler is a Grant vortex pro 36/46

it doesn't seem to be the thermostat as i have been checking all day now and even before the house is up to temperature the boiler still cycles!

thanks

Mike

 

[mpooley]

I have been checking some more and found that the boiler was set to low so I tried setting it to its highest possible (without new jets) which is 42.5kw.
This makes it cycle even quicker about 1 min on and 1 min off !

I wish i could work out what this means but I am baffled !


help please

Mike

 

[D_Hailsham]

It is a Danfoss TP500

Do you mean the TP5000 programmable thermostat? If so, is it the wired or wireless version?

 

[mpooley]

It is a Danfoss TP500

Do you mean the TP5000 programmable thermostat? If so, is it the wired or wireless version?

Yes I do
its the wired version

thanks

 

[kevplumb]

I have been checking some more and found that the boiler was set to low so I tried setting it to its highest possible (without new jets) which is 42.5kw.
This makes it cycle even quicker about 1 min on and 1 min off !

I wish i could work out what this means but I am baffled !


help please

Mike

it means the boiler is producing more heat than the system can disperse

 

[JohnD]

how hot are the radiators getting?

can you feel the pump, and is it hotter than the pipes?

 

[D_Hailsham]

it means the boiler is producing more heat than the system can disperse

Have you had this problem since the boiler was installed or has it only just started to happen?

How was the size of your boiler determined?

 

[mpooley]

it means the boiler is producing more heat than the system can disperse

Have you had this problem since the boiler was installed or has it only just started to happen?

How was the size of your boiler determined?

I think It has always been like this. I never noticed it before but my wife had. she just didn't think it was a problem.

The pump is working ok and its not hotter than the pipes. It is a bigger pump than usual.

as for sizing My plumber said that i should match the size of the old boiler that was here.

I have done some more checking - I didnt manage to get up before the heating came on but only 20 mins after turning on this morning, it was cycling ! and the rads were all hot.

I have listened to the thermostats and they are not causing the cycling as far as i can see. They usually click when the temp is reached and a burner symbol comes on.

I can see that if the boiler is over sized it will reach its max temp quickly and turn off but why does it turn on again so soon?

if it IS oversized then surely the heat will not be lost quickly to the rads and the return temp will still be high. in my ignorance of how the boiler decides when to turn on again I would have thought that it would wait untill the return temps were at least 20c below the boiler output temp?

thankyou all for trying to help

Mike

 

[Agile]

This sounds like a classic case of an over sixed boiler.

42 Kw is a lot of power! is it a very big house? 10+ bedrooms?

Tony

 

[mpooley]

This sounds like a classic case of an over sixed boiler.

42 Kw is a lot of power! is it a very big house? 10+ bedrooms?

Tony

It is Big - 5 big bedrooms -games room -study- large double floor hall - large kitchen- large conservatory - lounge - dining room - 5 toilets/shower/bathrooms + utility room
it is an old barn conversion. pretty good insulation though.

Mike

 

[D_Hailsham]

What type of heating - radiators or underfloor?

If radiators, and they are the typical flat steel type (with or without fins), use the Stelrad Elite Catalogue to work out the approximate total radiator output. Add on 3 or 4kW for hot water, as you will probably have a very large HW cylinder with so many bathrooms etc, and you will get the approximate boiler size you need.

This assumes that a detailed heat loss calculation was done when the barn was converted, so the rads are correctly sized. You could check this by using the Stelrad Stars heatloss programme - do a google and download it.

 

[mpooley]

What type of heating - radiators or underfloor?

If radiators, and they are the typical flat steel type (with or without fins), use the Stelrad Elite Catalogue to work out the approximate total radiator output. Add on 3 or 4kW for hot water, as you will probably have a very large HW cylinder with so many bathrooms etc, and you will get the approximate boiler size you need.

This assumes that a detailed heat loss calculation was done when the barn was converted, so the rads are correctly sized. You could check this by using the Stelrad Stars heatloss programme - do a google and download it.

I have just measured all the rads in the house and went to a rad site to work out the outputs.
The best I can work it out is approx 30.370kw plus 25 sq meters of underfloor heating which i dont know how to work out.

oh and 4kw for the hot water makes it 34kw approx plus the floor

this does not take into account that 4 of the bedrooms are turned off most of the time.
so I suppose im not using all that very often.


thanks

Mike

 

[iep]

I don't claim to have the knowledge of the other guys but the oversized boiler explanation makes sense to me.

Since it is not too cold yet and you do have a very powerful boiler (with some rads turned off), the system will get up to temp very quickly (within 20 mins).

Once the water in the system reaches the desired temp (as specified by the boiler's internal thermostat) the boiler will switch its burner off but leave the pump running in order to keep circulating water around the system. Then, because you have quite a large number of rads still running, the water will cool down pretty quickly. It does not have to cool down too much before the boiler's thermostat triggers and starts it up again.

Given the power of your boiler it will then heat the water up very quickly and the cycle will repeat.

To reasure yourself that all is well, turn the house thermostat down and wait for the system to properly cool down (about an hour). Then turn the thermostat back up and see what the boiler does when the water in the system is cold. If it still cycles during this initial heat-up phase then there may be another issue.

iep