Heating system's bypass valve in wrong place?

[Jaime]

Hi. I've finally identified a strange copper pipe connection between the flow from and return to my boiler as being a bypass circuit (with a gate valve halfway along it).

From what I've read recently, bypass circuits are designed to protect the pump in case the valve is open to the central heating circuit but all the trvs have shut down. Looking at the four or five schematic diagrams that I've seen, they all have the components in the following order:

Flow from boiler V Pump V Bypass circuit (back to boiler) V Valve

This makes sense to me - if the valve has effectively closed, the pump can still work by sending water around the bypass circuit back to the boiler.

Here's my setup - it's an open vented fully pumped system with the following bits:

Flow from boiler (Potterton Suprima 60L) V Bypass circuit (back to boiler) V Pump (Grundfos Selectric) V Valve (Sundial Y-plan V4073A1039)

Now, paraphrasing Snoop Doggy Dogg, "I ain't no plumber" - but this looks wrong to me. If I close the valve down completely, the pump won't be able to continue, because it's not included in the bypass circuit.

Only one question for the time being: is my deduction correct?

[Ian Stirling]

I have not looked at the manual for the boiler. Is it possible that it's a large circuit, and the external pump is simply supplementary to the built in one? In which case of course, there is no problem.

[Jaime]

I've looked at the "Installation and Service Instructions" for the Potterton Suprima 60L boiler and both of the schematic diagrams show the external pump included in the bypass circuit (i.e. flow from boiler goes to pump goes to bypass circuit goes to valve). Also, the boiler documentation says nothing about a built-in pump...

[Andy Hall]

Sounds like it, although the purpose is to keep a flow of water going through the boiler to prevent so that when the valve closes, the water doesn't become stationary and hence boil.

[Ed Sirett]

Suprimas do not contains integral pumps the OP's set up is wrong. Depending on the nature of the bypass ('smart' valve or 'dumb' gate valve) and the nature of the rest of the heating circuit (S-plan, or Y-plan, TRVs all/none/most) you may or may not get some over-run circulation as needed.