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boiler cycling every 2 mins

Discussion in 'Plumbing and Central Heating' started by peterm1, 17 Mar 2006.

  1. peterm1

    peterm1

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    Hi.I have Ideal mexico 2 125cf boiler.Once the heating and water reaches the desired temperatures the boiler kicks in for 2 mins then shuts down for 2 mins ,this continues indefinitely in auto or manual mode.I have replaced the boiler stat and thermocouple, room stat,a new programmer , but still keeps cycling every 2 mins.The radiators and hot water are absolutely fine(3 floors).Could someone help?

    peter :cry:
     
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  3. scatmanjohn

    scatmanjohn

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    Bit confused....

    First of all why have you replaced all them parts for no logical reason?

    Are you saying that when both the cylinder & room thermostats are satisfied the boiler is still firing up.

    Try turning them both down to minimum to see if it still fires up

    Let us know that bit first.

    Also let us know if you have any zone valves or a 3 way valve on your system.
     
  4. peterm1

    peterm1

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    Hi thanks for your reply.This is a long story so here goes,this problem occured a few days ago ,the plumbers are tied up for weeks(all of them)so they say,so i phone the plumbcentre and speak to their top guy(so they say)i explain the problem about the boiler cycling ever 2 mins.It sounds like a stat problem to me (he says),to be honest i thought so too,hence the replacement of stats.On the same day the boiler kicks in without the programmer calling it(bypassing the programmer).Shocked by this I call a qualified electrician(recommended by a friend) he suggest the programmer is faulty(the old one is about 15yrs old) so he called the next day and fitted it .We tried it and everything seemed to be ok.Until today that is.

    Both stats are satisfied even at lower settings the problem still exist.

    I have two motorised valves on the system.
     
  5. jobloggs

    jobloggs

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    Cold be a very sensitive room stat with little difference between demand and satisfied temperatures. Is it digital of traditional wheel type?
     
  6. peterm1

    peterm1

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    Hi, its a new honeywell wheel stat.
     
  7. jobloggs

    jobloggs

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    Do you have thermostatic radiator valves in room with watt stal by any chance?
     
  8. peterm1

    peterm1

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    The wall/room stat is in the hallway where i have a radiator with the valve on fully opened(5).
    The problem occured about 5 days ago,plus its the same cycle even if i run the hot water only.[/b]
     
  9. scatmanjohn

    scatmanjohn

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    I like this bit

    :LOL: :LOL: :LOL:


    You will find the fault is with one of the zone valves.
    They have a permenant live feed into them (grey wire)
    When you turn on the heating/water the valve opens up which sends the live feed to the boiler down the orange wire.
    If the valve sticks open the power is still sent to the boiler even when the programmer is off.

    jobloggs...He has said that the programmer is NOT calling so why would it be the room stat?
     
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  11. peterm1

    peterm1

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    Hi , I am glad someone can laugh about this (although I did have a chuckle myself when reading it again). :D :D
    Is there a way off testing the valve or is an electrician again :!:
     
  12. Nige F

    Nige F

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    Well I learned summat today and I thought you were full o` scat ;) Does this happen with 3way valves too?
     
  13. scatmanjohn

    scatmanjohn

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    I'd be inclined to say get the electrician back who fit the new clock.
    You have already paid him for something that you didn't need.
    Ask him to check if there is 240Vac on the orange wire of each valve when the CH & HW is turned off at the clock.
    Its a bit of a bugger if its intermitant.

    If you want to have a go yourself you need to be able to confirm safe isolation of the power before touching it. Do you have a multimeter
     
  14. scatmanjohn

    scatmanjohn

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    No ;)
     
  15. Nestor_Kelebay

    Nestor_Kelebay

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    Would the motorized valves you have on your heating system be Honeywell also? I'm familiar with Honeywell V8043 series of motorized valves for hot water heating systems which are as common as a barking dog over here, but not with the 3-way models that seem to be commonly used in the UK.

    I'm thinking that the reason why the plumbing contractors you spoke to suspected a thermostat problem is because Honeywell thermostats (and I expect all thermostats) have something called a "heat anticipator" in them, which is nothing more than a small electric heater that heats the bi-metallic spring inside the thermostat to fool the thermostat into shutting off the heat early.

    The reason why you want to fool the thermostat into shutting off the heat early are several:
    First off, on a hot water heating system the cast iron radiators are going to keep convecting heat into the room as long as the water in them is still hot, NOT just when the thermostat stops calling for heat. So, you want the thermostat to shut the boiler off earlier so as not to overshoot the thermostat set temperature too much.
    Secondly, the radiators are located around the perimeter of the house, whereas the thermostat is centrally located. If you waited until the air temperature at the thermostat reached the set temperature, the average temperatue everywhere else in the house would be higher than that.

    Typically, the way a heat anticipator works is by having a variable electric heating element situated right next to the bi-metallic spring and wired IN SERIES with the mercury switch so that the heating element only works when the thermostat is calling for heat.

    As you may have already guessed, the heat anticipator setting also affects the boiler cycling rate. A very low heat anticipator setting will cause minimal heating of the bi-metallic spring, and a lot of overshoot of the thermostat temperature setting and a excessively long boiler cycling rate.

    Conversely, a very high heat anticipator setting will cause rapid heating of the bi-metallic spring, thereby fooling the thermostat into thinking the whole room is already hot and shutting the boiler off soon after the boiler comes on. But, since the room air isn't actually warm, the small bi-metallic spring cools down quickly, causing the thermostat to call for heat again right away. Thus, too much heating by the anticipator will cause the high boiler cycling rate you seem to be noticing.

    I think digital thermostats do the same thing electronically, but I don't know anything about digital thermostats, so I can't say for sure.

    Maybe investigate the possibility that the heat anticipator setting may be the culprit as well.

    http://yarchive.net/electr/thermostats.html
     
  16. scatmanjohn

    scatmanjohn

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    The poster has already said that the boiler fires up when the clock is turned OFF.

    Unless an s plan is wired up differently in Canada i can't see how you would think it was the room stat.

    Also if you have read what has been said already you would see that he has replaced
    Programmer (Electrician Guessing)
    Room stat (?)
    Boiler stat (cos the man at the Plumb Centre said so)
    Thermocouple (God only knows why)

    :rolleyes: :rolleyes:
     
  17. peterm1

    peterm1

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    Hi,Well here we are again with the same old problem.The electrician tested the programmer and the motorized valves.The programmer heating side and valve on the heating both faulty,(what a coincedence) so we have replaced,brilliant :LOL: .
    Guess what :?: ITS STILL F-----G CYCLING EVER 2 MINS ON THE HEATING. :evil: :evil: :evil:
    Which so called experts do i call know :?:
     
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