Unvented wiring 2 port safety valve?

[bster]

Installed a Santon Prem Plus in college today and whilst wiring up i realised that i was missing the Santon control relay - my tutor said 'dont worry just wire from HW ON to the cylinder hi-limit stat then back to the wiring center to switch the 2 port,3-port, boiler and pump.

Is this correct? - why do i need to use the control relay? (which i'm guessing that you have to).

BTW its a 3-port and 2-port set up.

 

[Paul Barker]

You have to use a 2 port valve in series with an unvented cylinder, so that in the event of a power cut the valve fails in the off position and therefore the cylinder will not overheat and explode (should all the other safety's fail). If the rest of the system is S plan then the two port valve from the s plan is sufficient. If Y plan you MUST add in the two port as the mid position valve does not fail safe.

Also beware that some 2 port valves on the market don't either. You must use one which is sprung shut in the event power is cut.

 

[gas4you]

All unvented cyls that I fit come complete with 2 port valve. Do not all makes?

 

[Paul Barker]

Yes, but they aren't all supplied with the correct fail safe valve. I don't recall the make now but I did fit one where they supplied a valve which requires power to move in both directions. I of course fited a suitable valve and informed the manufacturer of their error at the time.

 

[bster]

yeah i know why you have to incorparate a motor on\spring return valve for unvented but i am wondering about the Santon relay that the MI says you need to use when using a 3port and a 2 port valve but not when you s-plan it.

What does the relay do that wiring a 2 port in series with the hi-limit stat doesnt?

cheers

 

[doitall]

Yes, but they aren't all supplied with the correct fail safe valve. I don't recall the make now but I did fit one where they supplied a valve which requires power to move in both directions. I of course fited a suitable valve and informed the manufacturer of their error at the time.

MHS Gemini ring any bells Paul