Actuator or not?

[davecash]

I have a Potterton Suprima boiler. I have overheated water all the time, either when the CH and HW are on, or even when just the CH OR HW is on. Have repaced the strap-on tank thermostat. No luck. An amateur plumber I know has suggested I get a replacement Actuator MSV322 (he called it a 3 way valvehead). Can anyone advise me if this actuator is likely to cure the problem or not.
Thanks.

 

[seco services]

is the cylinder stat switching off when temp reached ?
what is the stat set to ?
is the flow pipe from the 3 port valve to cylinder hot when only heating been on ?

can only really be the stat or the valve not shutting fully when heating on only.

 

[davecash]

Thanks for swift response.
Yes, cylinder stat clicking at appropriate temperature (it's brand new). Tried the new stat on 40 and 60 but water still boils up whatever I do.
Can't answer your third point at moment as I have switched everything off. Frightened that tank will blow it's top!!

 

[seco services]

did it use to be ok or has it started since someones tampered with wiring ?

 

[davecash]

It used to be ok. No wiring tampered with, other than to fit the new tank stat - after it started to boil up.

 

[seco services]

so if you only have hw on and turn the stat right down the boiler is still kicking in ?

if so i would check the switch live from the stat to see if its not live when stat turned down and live when stat turned up.

 

[MANDATE]

Hi Dave! Not too sure what you mean by overheated water.
If it's hotter than you would like coming from boiler then why not turn the boiler stat down. If you mean the hot water is too hot in the cylinder then turn the cylinder stat down.
The cylinder stat when 'satisfied' cuts the electrical supply and it switches boiler off if on HW only.
If on HW and CH it does the same, but it also moves the valve to CH and relights the boiler.(but not from the cylinder stat)
The valve does nothing more than direct the water to the right place according to what is being demanded and what is satisfied. So I can't see replacing the actuator head will solve it.
I had a situation on same boiler, where 'kettling' occurred. The water in boiler was being boiled and not being replaced with cooler water quick enough. On removal of pump the 20mm inlet and outlet holes had a build up of 'crud' making the holes about 6mm diam. So this created a resistance that pump could not cope with.
Maybe you should start with a thermometer on the boiler flow pipe and prove the boiler stat functions.

 

[davecash]

At the moment, the Actuator is unscrewed from it's position. Have just checked HW only. With tank stat on normally (60C) boiler flashes up. When turned right down, boiler goes off.

 

[davecash]

Hi Mandate,
Thanks for contribution.
The temperature has never been altered on the boiler (it's just under half way). The water suddenly started to get exccessively hot for no reason. Tank stat was set at 60C, which I understand is 'normal'. Tried it at 40C next day - still boiling water. Fitted new tank stat. Set it at 40C to begin with - still boiling water. That's where I am at present.

 

[seco services]

so the stat is working ok. its cutting in out.

 

[davecash]

Yes, it would appear that the tank stat is working, clicking on and off, but if I leave everything at normal, the water still boils. It ignores the tank stat.

 

[seco services]

if the stat is working ok and cutting the power on/off then the boiler can't fire up if the stats reached temp.

is the stat sitting on the cylinder properly ? or it won't detect a heat rise.

 

[namsag]

Make sure boiler burner is going completly off and that it is not staying on a little bit. ie gas valve passing

 

[davecash]

Thanks everyone for your contributions. Greatly appreciated. I will try some of your suggestions over the next couple of days.
I may be back!!!!!

 

[MANDATE]

If you have got as far as removing the head, you may as well check the valve spindle for stiffness. Also you can watch the underside of the head (D shaped hole) while you try the various positions to ensure it moves correctly, when the demands are satisfied