CH automatic bypass valve and filter

If you were to fit a variable pressure pump (that detects the TRVs closing and reduces its output accordingly) I *think* the bypass might be less significant? I guess it might still be required for pump overrun.

If your boiler doesn't need an over-run (pump and boiler call-for-heat wired in parallel) then you don't need (i.e. shouldn't fit) a bypass if you install a modulating pump. If the boiler controls the pump then you can fit a modulating pump but need to wire an additional valve ... Search for W-B TB0074 for more info.

It?s a Grundfos UPS3 which has some smarts. I?ll need to do a bit of reading I think.

Tim

I installed one of those last year. As the gate valves were seized up and the new ones were a different size I needed to adjust the plumbing. I removed the bypass valve on the basis that the new smart pump should look after the situation with all TRVs closed. It all worked fine. However, when I removed the bypass valve I discovered that it was so clogged up with crud that it couldn't have been working for years.

John

In my experience, automatic by-pass valves and smart pumps don't make good bed-fellows. Smart pumps reduce their speed when the flow is restricted due to TRVs and/or zone valves closing in order to maintain a more or less constant pressure. But automatic by-pass valves *need* an increase in pressure in order to open. If they *don't* open when they should, there'll be insufficient flow through the boiler to stop it overheating from residual heat during the pump over-run phase after it has stopped firing.

I found it necessary to disable the smart features of my pump, and use it in manual mode.

IME using the modulating mode makes a significant difference to the flow noise as radiators are shut off. Have a look at the TB I referenced earlier.

I've had two Honeywell DU145 auto bypass valves fail in the last 10 years. Bloody things fail open, or partly open, so hot water is flowing through the bypass loop even when the zone valve(s) are open. I seem to recall reading somewhere that building (or some other) regs mandate a bypass valve in CH systems. Can't find the reference now, so don't know if true. I'd thought about putting a normally open version of a zone valve in the bypass loop, driven closed by the boiler call signal from the CH & HW valves, so whenever there's a call for heat the bypass closes, otherwise it stays open (including on pump overrun). Dunno if the micro switches in the CH & HW zone valves would handle the additional load though. (S-Plan system btw).

I'd also thought of doing that, but have never got round to it. The use of a diverter valve mentioned elsewhere in this thread would achieve the same result, possibly in a slightly more elegant way.

What's happened to the idea that towel rails act as the bypass? May not be as efficient - in theory - but far more reliable.

As in, "the component that's never fitted is free - and 100% reliable".

PA

Easily. The microswitches are typically rated at least 5 to 6A and can be higher depending upon make. The additional valve will take about 7W, so an extra 30mA.

Thanks Steve!

Oh well, I?ve deleted by bypass gate valve for the moment and fitted the new pump.

So far all seems well and the radiators are heating more quickly and better than they?ve done for years AND the pump is a lot quieter. I found that the old gate valve was letting a lot of water past even when supposedly closed and I suspect that it was significantly slowing the system warm up time as the return flow to the boiler was reaching target temperature way too quickly.

As ever with plumbing there were a lot more buggeration factors complicating what should have been a simple job, some of my own making and some just daft design. I mean, why put all the boiler?s electrical connections in a box screwed to the underside of the boiler (with Torx screws)?

As my boiler is in the loft only 8? above the loft floor this was a PITA.

I have fitted the new pump in a ?non-standard? position and this may come back to bite me in the bum but I?m prepared to chance it. It?s now by my HW tank pushing water up to the boiler in the loft via the boiler return rather than being in the loft on the flow side (where it had very little head of pressure and would cavitate whenever the system pressure dropped.

Time will tell if this is a mistake (or everyone on USENET). ;-)

Tim

Sounds like a neat solution. Must look into this.

Tim