Unvented Water System Question

[IanDB]

I've asked this one before but it was a long time ago.....

I have a Megaflo system. On the flow side of the heating coil there are two zone valves in series. One is a Honeywell, the other is a Sunvic (next to the tank). The Sunvic one burnt out a while back and was causing the pump to run continuously. I took the actuator off and have yet to replace it. However, the sytem runs very well without it and I cannot understand its purpose. My boiler was serviced recently and the guy was adamant that it was a safety feature but he coudn't explain why. To my way of thinking it only added unreliability as it was in series with the exisiting hot water zone walve (both electrically and hydraulically). Megaflo say that the zone valve supplied with the tank must be used but I'm wondering whether this was meant to be instead of the other zone valve rather than as well as.

Any ideas?

 

[seco services]

5.2 INDIRECT THERMAL CUT-OUT AND 2-PORT MOTORISED VALVE
To comply with Building Regulations and to prevent the Premier Plus from overheating the 2-Port
motorised valve supplied fitted to the primary flow to the indirect coil MUST NOT be removed or
bypassed. This valve is factory wired in series with the indirect thermal cut-out such that the primary
flow to the heating coil is interupted should the Premier Plus SystemFit unit overheat.

 

[IanDB]

So my suspicion that it was never wired correctly in the first place could be confirmed. The Megaflo system is not factory wired - installed locally.

I'll check with Megaflo.

Thanks

 

[simond]

On the contrary, it is likely the zone valve was wired correctly. I take it that the Sunvic is a 2 port and the Honeywell is a 3 port?

 

[IanDB]

Nope, they're both two port. The Honeywell is a V4043H and the Sunvic is one of the SZ23XX series (I'm trying to find out which one).

Having looked into this in some more detail, am I right in thinking that the actuator should be linked to the high limit or energy cut out thermostat? If so, that's aother problem as the only high limit switch is embedded in, and integral to, the boiler.

 

[simond]

The high limit switch you refer to is inside the Megaflo, not the boiler.

It should be wired in series with a spring closing motorised actuator to cut the hot water primary from the boiler in the event of an overheat situation.

 

[IanDB]

Yes, I agree. I assume the high limit thermostat is in the same area as the main tank thermostat. I haven't had a chance to look yet. However, as I've said earlier, this was never wired in originally. When the actuator burnt out the first time round I traced the wiring back and found it to be wired in series with the hot water zone valve, hence the decision to leave it off as it didn't seem to do anything. It would appear that whoever did this (a long time ago) didn't know what they were doing and have left me with an unsafe installation. I suppose it's just as well to find out now rather than when things go wrong.