A friend of mine has called me with probs since his megaflow has been plumbed in. System as follows. Y-Plan Megaflow with additional 2-port to comply to regs Vented heating circuit. Problem is HW side. Once system is calling for HW only, when HW reaches temp the 2-port closes but system keeps on running & causes pumpover on F&E tank & them overheats. Electrician has checked wiring all OK Anybody else suffering same prob/any ideas?. Stitch
Y-plan uses a 3-port mid-position valve. You can't use a 3-port on it's own, because the DHWS port is open when the power is off. So he has added the 2-port zone valve to the pipewrok on the DHWS outlet port of the 3-port valve. I'd think he had just made a hash of the wiring. The Honeywell wiring diagrams are here, http://content.honeywell.com/uk/homes/systems.htm but you'd need to work out how the additional wiring should be added to the existing 3-port wiring actuator. It would be a more sensible idea to change it to S-plan wiring (two 2-port valves). It's more reliable than mid-position valves and the nest person to work on it will be able to find a standard wiring diagram.
It does read that it has never worked, get a different plumber or electrician in. I agree with 1t it sound suspect.
Its a simple wiring modification needed. In words a competent person would just wire the switch in the two port in series with the HW switch in the three port to end the call for heat. Thats the simple modification to make it work! Tony
so what happens when the two port closes?, the heat from the pump over run has to go somewhere, it cant go to the ch because the 3 port is closed, the pump is just running against a closed circuit, it needs a bypass
SJ,I cannot understand why plumbers go for a Y plan on unvented systems,it is not recommended.Replace the mid position valve & convert to S plan,there is only a small alteration to do on the wiring up.Have you checked the the wiring from the two port valve back to the electric control box where the thermastat is.It is obviously a electrical fault along with a bad plumbing installation;(