Worcester 15/19 oil boiler, problems with new thermostat

[Aquaheat]

@Peter.N. Did you try this suggestion?

Immerse the stat phial along with temp gauge into a pan of water and bring to the boil , should rule out stat or not..

A very simple test that will completely rule out at least one issue. You can then start diagnosing from there.

Has any work been carried out on the system, boiler or house in general especially with regards to electrics or controls? The stat may actually be working but you could be picking up a live from elsewhere maybe?

 

[Peter.N.]

I hadn't thought of that John I just did and it was empty. The ball valve is fed from and old supply pipe that comes from the farm, its an emergency supply in case our well runs dry. Earlier in the year I found I was losing about 100 gallons or more of water a day due to a leak somewhere under ground so I disconnected it and thought no more of it

I have now filled it with a watering can and the air in the pump has gone but it hasn't made much difference to the cut out point. I will give it a while to purge the air and see what happens.

Aquaheat.

Thanks for your suggestion, used to do that with car thermostats, I didn't try it with this one because the replacement stat arrived and I fitted it with the same results. I have stood there while its warming up and listened for the 'click' but there isn't one, it does however cut out if you turn the boiler off and go away and leave it, you can then rotate the stat and hear it clicking on and off, but once it gets cold and you switch it on it goes up to about 80C again.

If it doesn't work now its full of water I will try your suggestion.

Peter

 

[Aquaheat]

Not my suggestion @Peter.N. it was @Steelmasons but it will 100% take one thing out of the equation. @Burnerman knows his onions but diagnosis means doing the simple things to prove their function (or not)

It is highly unlikely that you have two faulty stats but not unlikely that you have two incorrect stats. Prove the simple things first and work your way through. If, as you say, the stat does not "click" out then I would be asking why. Do you have a multimeter and are you confident to use one?

Jon

 

[Peter.N.]

Hi Jon

Sorry about the confusion - its the age The stat appears to be OK because if you turn the boiler off and wait a few minutes it will turn on and off, until the boiler cools down again.

I know about stats, I was a TV and electronics engineer for 50 years, John was also in the trade I believe, very useful when working on car electrics although electronics has passed me by now, I grew up with valves.

 

[Steelmasons]

Remove the stat phial from phial pocket and affix it to the heat exchanger in close proximity to the pocket using foil tape or similar.
Temporarily link out high limit stat in order to rule it out , fire burner and note results.
Could well be high limit stat although without checking for continuity across all 3 stat terminals (overheat being a manual reset) to determine which stat is satisfied/calling then you're pizzing in the wind.
This issue could be diagnosed within the time it takes to make a cuppa.
Have you removed all 3 stat phials from pocket and checked/cleaned?...operating stat phial sits inside hi limit/manual overheat phials.
Check the basics.
Take note that ALL 3 stats are wired in series..

 

[Aquaheat]

What he said ^^^^^^

Stop looking for things until the basics are ruled out!

If you have a probe stat then that would help too as you can actually check the temps.

 

[Steelmasons]

He won't acknowledge me for some reason Jon..

 

[Peter.N.]

HI steelmason

Sorry I wasn't ignoring you but I attributed your first message message to Aquaheat, another senior moment, and I have only just seen this one. Yes I am aware that all three stats are wired in series, the variable stat is switching the boiler off but at a much higher than normal temperature, if you turn the boiler off when the temperature reaches about 70C and leave it off for a few minutes the stat switches off, you can rotate it and hear it switching on and off, if you leave the boiler on it will eventually cut in again and the water temperature is about 50C which is fine, once having come on it now won't go off again until it reaches about 80C.

I was going to try placing the sensor on another part of the boiler but haven't got round to it yet

Peter

 

[Steelmasons]

How much movement does it take for stat control knob to switch between on/off (hysterises)?..try this with and without control knob fitted.
As above have you pulled out the other two stat phials and inspected them (Spring coils)?

 

[Peter.N.]

It depends on the temperature but when it near its coolest about 5-10 degrees of rotation will make it change state which I would have thought corresponded roughly with the +- 5C specification. It seems that its taking the stat a long time to reach the boiler temperature, when it eventually does it will switch off but not on again until its fairly cool, it seems as though either the heat is not being transferred quickly enough or the temperature of the sensor cavity is lower than the rest of the boiler.

Peter

 

[Terrywookfit]

F F S !! Have you considered measuring the ACTUAL temperature of thermostat pocket ??

 

[Peter.N.]

Yes, but I don't have anything to measure it with, I have ordered a clip on thermometer to check the pipe temperature, I have a meter with a temperature probe but I don't think its very accurate. Anyway I have now put the kitchen back together, the boiler is buried under the worktop behind the dishwasher, my wife wants her kitchen back so until I get my temperature gauge I can't do much more.

We are managing with the boiler as it is but you just have to be careful not to loose a few layers of skin when you have a shower.

I will do as you suggest though and check the temperature of the pocket.

Peter

 

[Aquaheat]

I've just had a week and abit away with the family which was wet and windy most of the time! (weather not the missus) I'll come to Dorset and sort it for you for accommodation, a big mac meal and hot water that doesn't scold me!

 

[Peter.N.]

Thanks - watch this space.

Peter