Boiler permanently on

Discussion in 'Plumbers' Talk' started by Graham price, May 31, 2011.

  1. Graham price

    Graham price New Member

    Hmmm.  As usual, a lot of  sense in what you have to say.  I have just used the hot water and it's much hotter than it should be which concurs with what you said about the boiler modulating.  Getting to everything to play with a multimeter is quite difficult because it's all at the back of a big airing cupboard, including the programmer which the electrician promised to move but of course never did.  That's why I can't hear if the microswitch is operating or not. I'm tempted to take a gamble and replace the valve.  It's not mega-bucks after all and at the very least it would eliminate a suspect.  Is it much of a job ?
  2. You'll need access to the wiring box. Also, the system will need draining and refilling afterwards - not a dificult job, but could be 'worrying' for someone who's never done it before (fear of floods, etc! Other than that, it's generally just a case of slackening 3 nuts. If the actual valves are moving ok, then it's possible - or some units at least - to just replace the motor/switches unit, so no water touched. Much easier. And the valves should be ok on a 5-year old system. Have you checked the colour of the system water recently - by loosening a bleed screw? Is it clear? Just wondering if there's sediment in there that could be affecting the operation of the valve - unlikely it's that, tho'.

    Bear in mind two other things - one, I'm only guessing it's the valve, and two, I'm not a plumber....

    "Oh sh**..." I hear you say...
  3. Graham price

    Graham price New Member

    Thanks once again; you deserve a medal.  Before I do that I had a think (at about 2.00 am )  Is there a device which is "king" and is able to over-rule everything including the stats ?  When the fault appeared it was the middle of the night and the HW was programmed to come on about 6.00am or so.  You will guess I'm thinking about the frost guard.  I understand there is one in the boiler and also there is a separate one near it.  It's the over-riding of both stats which is bugging me.  I have to say that nothing ever happened over the winter when it was much colder of course but could one have developed a fault ?

    That question asked,  I notice that now whatever I do with the valve lever the system just comes on with the main switch; I don't get the half second run I did when you first suggested I move it about.
  4. Hi Graham. As far as I know, the frost 'stat in the boiler will only serve to keep the boiler itself from being damaged by frost - it won't send water around the pipe work as it can't control the valve (which it would need to do. (Afaik)

    The basic 'block' sequence  of control is (afaik) : main switch (which should be a SINGLE isolating point for EVERYTHING to do with the CH system) > programmer > room 'stat (or cylinder) > motorised valve > boiler switch. The boiler (depending on model) will also have a permanent power supply (but which is also isolated by the single main switch.)

    Therefore, the programmer is 'king' and nothing else should get a switching signal unless first delivered by this item. Shorting out the room or cylinder 'stats won't turn the system on unless the programmer is supplying an 'on' signal in the first place. Ie: the 'stats are fed from the programmer.

    However, the motorised valve can also act as 'king' and switch on the boiler and pump if it's faulty - even if it isn't getting a live feed from the programmer. This is because the valve has its own permanent power supply as well, and you can demonstrate this yourself by manually moving the valve lever; the boiler and pump will turn on even if the programmer is saying 'non'. That is why I suspect the valve more than anything else.

    If the programmer was the faulty item, it still wouldn't be able to trigger the system unless the 'stats were also 'on' - it can't override the 'stats.

    (Many room 'stats (espec programmable types) have a 'frost' setting, but even this can't do anything unless the programmer is also 'on'.)
    911_Bob likes this.
  5. Graham price

    Graham price New Member

    Now I understand why you suspect the valve.  I work in the steel industry and we have to do a lot of problem solving using Kepner Tregoe  eg. you can't climb into a blast furnace to see what is happening.  I've been trying to arrive at the "only if" point.  It seems that the only bit of kit which can over-ride everything is the valve.  It also contains some electronic bits which I guess can develop a fault at any time they have a live feed.

    Looking at the valve looks much the best option.  I'll have a decco later on and see if it's possible to replace the outer bits.  I may be back for some more advice if your patience will stand it !

    Many thanks again
  6. Patience ma botty. Anything beats watching the tumbleweed on here...

    Anyways, what make is the valve?
  7. I think that me using "What make's your motorised valve?" as a chat-up line fully explains my success with women.

    And some peeps on here might know if the motor part can be replaced independently.
  8. Yes, that did tickle me :)


    Not that I care.
  9. Anyways, it's a helpful...
  10. Graham price

    Graham price New Member

    The valve is a Honeywell.   Should I count this as a "helpful" too ? 
  11. So it should have a removable head.

    However, I will remind you I am not a plumber, or a sparky, or a chippy, or a welder, or a cook. So it's up to you to have any of the stuff above^ confirmed before you decide to replace the gubbins. A complete valve is around £60+ I think; what the 'top' part costs I dunno.

    Whatever you do, enjoy...
  12. Graham price

    Graham price New Member

    I think that, thanks to your patience, I have arrived at the point where I have to replace the head.  Like you, I'm not any of the things you mentioned ( I'm a metallurgist ) but I think I know a logical thing when I see one.  Next step is to do some research to find the appropriate bits.  If it solves the issue I promise I won't give myself the points for a correct answer  ( dunno how I did that.................)  I'll let you know in due course.
  13. caseyboy

    caseyboy New Member

    Don't waste money on new m/v head or motor or programmer. Check the wiring center with a multi-meter. If your getting aprox 100 volts on the white wire( heating supply to m/v) then your getting a residual voltage, probably from the pump over-run. This will only happen when you turn on the C/H . The answer is to fit, between the switched live (usually terminal 8 on the Y plan) and neutral ( usually terminal 2) a 0.47 uf supression capaciter. Cost pennies.  For information purposes, Honeywell valves can be rebuilt without draining down. The motor only is replaceable (one small screw, two wires) or the complete head can be removed from the body and replaced.
  14. Hollick93

    Hollick93 New Member

    You are on the right track there G. 9/10 times the head is the issue. Microswitches and moving parts...etc. Great thread AD
  15. Deimantas

    Deimantas New Member


    *. has extensive plumbing experience for domestic and commercial plumbing, gas central heating installation, refurbishment and repair, power flushing, bathroom installation and renovation. You can find out more about our extensive range of services by following the links on our website: * or calling us on *

    Message was edited by: Screwfix Moderator
  16. Graham price

    Graham price New Member

    The replacement head has arrived so I'm committed.  The wiring in the main box is so crammed I'm going to cut the original fly lead and use a junction box.  I will let you know if it works.  If it doesn't you probably won't hear from me because my wife will have executed me for trying myself.  Somehow she trusts me to mend cars but believes only plumbers can deal with heating..............................................
  17. Graham price

    Graham price New Member

    Well it's nil points ( you can do the french accent ) all round.  With the new head the system still stays on permanently.  My installer is calling later this week so watch out for an update from which we all might learn something.
  18. caseyboy

    caseyboy New Member

    Re my post of the 7th June. Did you look for a residual voltage on the white M/V wire ?. As I said then, once you operate the heating circuit the residual voltage will keep the heating port of the 3 port m/v open. Only by fitting a suppression capacitor between live and neutral will the problem be solved,me thinks.
  19. sam spade

    sam spade Active Member

    You seem to be going round and round in circles. Diagnosing a fault has to be done in a logical sequence.

    The steps are given in the link I posted on 1st June.
  20. blertsville

    blertsville Member

    My installer is calling this week , why didn't you do that in the first place....;...muppet

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