Potterton Suprima 70 & Myson Power Extra Valves

[oakland99]

when you turn the cylinder stat down or when it reaches temp does the hot water valve motor off, you said earlier that the hot water is on for three hours, it should reach temperature before that then shut off the boiler and the pump over run will kick in then shut off pump ..if this is not happening then h/w valve is sticking.. i've found those myson valves a bit iffy

 

[ollski]

Ollski

Sorry - I'm not with you? What are you saying then?!
When the tank fills with water hot enough to turn the stat off, the power valve closes and the pump overrun runs for a period of time as you describe...

This cycling problem I'm referring to happens prior to the tank reaching the stat temperature.

I was referring to this:

The pump never seems to stop running during the whole 3 hours or so I have the heating or hot water timned to come on....just a continual cycling of 5mins (ish) on...2 secs off.

If the sceario is only on demand I would imagine the hw zone valve is slipping back then motoring on to the microswitch again.

 

[nickso]

mondriver, are you saying that when the boiler is under demand (a valve is open and calling for heat) it will fire up and pump is ok until the boiler shuts the burner down, when the ignition sequence starts again this is when the pump stops momentarily?

if that is the case i find it unlikely to be a valve fault, especially as you have an S-plan system.

the boiler should directly control the pump with no interference from any valve other than the initial call for heat through the switched live wire to the boiler.

is the pump wired directly from the boiler?

does the switched live drop its 240v when the pump stops? (im betting no)

 

[mondriver]

nickso

The scenario you describe is exactly what happens.

The switched live does drop it's 240v when the pump stops for 2 secs.
Because of this, the only thought was a PCB fault. I've had 2 pcb's and the same fault occurs.

The pump is connected to the wiring loom in the boiler.

ollski

On re-reading your & my posts, I may be leading you astray!
This problem occurs for the duration of the timed heating cycle (3hrs), but the system is turned off as it should when the tank stat reaches temperature - opening the overrun valve for a few minutes etc. If the water temp drops in the tank, the system starts again and the 5min on 2sec off cycling starts again when the boiler fires up on a heating cycle.

 

[nickso]

nickso

The scenario you describe is exactly what happens.

The switched live does drop it's 240v when the pump stops for 2 secs.
Because of this, the only thought was a PCB fault. I've had 2 pcb's and the same fault occurs.

The pump is connected to the wiring loom in the boiler.
.

have you mixed up the switched live and pump live in your head? switched live dropping does not indicate a faulty pcb as power is going to the pcb not from it.


if the switched live drops out then it is a valve problem as its telling the boiler to stop heating. i dont believe this could happen though as the suprima simply isnt quick enough to switch back on after a two second drop of voltage on the switched live. the pump overrun would be on anyway and the suprima quite often sits with the green light flashing for 2-3 minutes after you switch it off and on....try it yourself, switch the demand off and back on again and ill guarantee the fault couldnt be replicated.

 

[mondriver]

have you mixed up the switched live and pump live in your head? switched live dropping does not indicate a faulty pcb as power is going to the pcb not from it.

Hmmm...not sure now...!

I've taken a volt reading from the terminals that the pump is connected to. 240v drops off for the 2 sec period.

I'm thinking you are talking about another point aren't you...?!

 

[superdupergasman]

Yes, he is talking about the switched live into the boiler rather than the supply to the pump.

Get a thermometer on the flow pipe, how hot is it getting.

As I have said all suprima's stop the pump for a second, when they re ignite during their ignition cycle, quirk of the boiler.

The cycle is not stopping as the boiler is not being told to stop during the 3 hrs, if the room stat does not click it off, it will go on and on and on for the full 3 hrs. Once everything is up to temp, it will be going off quicker. Likewise with the HW cycle, if the tank is not getting upto temp then the boiler will keep cycling for the 3 hrs.

 

[mondriver]

Thanks superdupergasman

I can't believe that the boiler is designed in such a way that it will cycle the pump off/on every time the boiler fires up...!

What a stupid system....

..isn't that just going to knacker the pump quicker than normal.

It's so annoying now that I'm conscious of the noise. It just sounds like it's faulty.

If you say that it's a quirk of the Suprima boilers...there's not much I can do about it apart from get a new boiler...which is pointless as apart from this annoyance - it works fine...!

 

[superdupergasman]

There is something slight amiss though if the boiler/pump runs for 3 hrs whilst heating only the HW.

A cylinder of HW should take no more than 60 mins to heat.

Thats why I was questioning,, the boiler stat, cylinder stat and boiler flow temps.

 

[mondriver]

Ok

Update for any of you that may have the same problem, or searched this is the forums.

The thermostat on the boiler was set to about 3 o'clock position by the British Gas man. He said that's where it should be left.

Today - I tried turning it up to max. ie:9 o clock position.

Guess what?

Problem cured....!

I can turn the stat on the boiler down to about the 7 oclock position and it still runs continuously (not stopping and starting every 5 mins).
Problem cured.

The tank of water now obviously heats up faster (about 35mins instead of about 45mins on the old setting).

I wonder how much extra gas I am burning due to turning the boiler stat up...
I guess if the boiler shuts off 10mins earlier after heating the tanks of water, that must cancel out the increased gas flow used by running the boiler at a higher setting...? Anyone?!

So - if you have one of these boilers, and have the problem described on page 1...make sure your boiler stat is turned up to max. Adjust then as necessary.

Best rgds

 

[D_Hailsham]

I wonder how much extra gas I am burning due to turning the boiler stat up...
I guess if the boiler shuts off 10mins earlier after heating the tanks of water, that must cancel out the increased gas flow used by running the boiler at a higher setting...?

Provided you have a room thermostat and a cylinder thermostat which turn the boiler off when the house/hot water reach the set temperature, you should not be using any more gas - in fact you could be saving it.

 

[nickso]

and the pump will still stop and start anyway.