Bypass valve position

What's this about having to fit a bypass valve to comply with building regs? Can't I just leave one rad without TRVs or isn't that the same?

Regardless I thought I would fit it at the 'manifold' end which is fed by a pair of 28mm pipes but is some way remote from the boiler. Is this a suitable position, or would it be better closer to the boiler itself?

Reply to
Jeff
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You are not allowed to fit a normal bypass valve. But IF your system requires a bypass it must be an automatic bypass valve.

If you have a rad without a TRV and can guarantee you won't turn it off then you should be fine.

That said, saying leaving just one rad sounds like you only have one heating zone which doesn't meet the building regs except in small flats. You need at least two and each would need a rad without a TRV.

Reply to
Mike

It's not just no TRV, it mustn't have any hand-operated valve. This would normally be in the room with the thermostat, as the roomstat then provides the heating control.

This just isn't true. I've looked round a number of new houses recently for a friend (3 and 4 bedroom), and I've never seen one with more than one heating zone. Zoning the heating is something really rather restricted to committed DIYers.

Yes, and you must ensure a water path remains after the call for heat is gone during the pump run-on period.

Reply to
Andrew Gabriel

depends on configuration of your system - see below

...

reference?

IIRC it's required for larger houses but I can't remember the size threshold or what reg it's in (part L, I'd guess)

thus a bypass is needed for an S-plan system but not Y-plan (where the 3-way mid-position valve provides a path via the HW cylinder)

Reply to
John Stumbles

Could you not still get into a problem situation though with Y plan?

If there was no call for heat from the cylinder stat, but there was from the room stat, the 3 port valve would have switched to the heating only position and eliminated the path through the cylinder. Meanwhile if there were TRVs on all rads (including the one in the room with the stat), then they could all close off but leaving the main stat calling for heat and no path through the CH circuit.

Reply to
John Rumm

Yep you are right

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Reply to
Doctor Evil

Ah, yes, I read about the multi-zoning as well but I forgot about that.

As a committed diy-er all my previous systems were multi-zone but as the first almost all TRV system I thought why bother. It's easy to incorporate fortunately. I think the property will count as big.

So - provided my system design and controls ensure a water path at all times that the boiler is firing, which I would have done anyway without really thinking it was anything special, I don't need a bypass, automatic or otherwise?

Reply to
Jeff

Not quite! You need a water path at all times when the *pump* is running - including any over-run period *after* the boiler stops firing - by which time all zone valves may be closed!

Reply to
Set Square

As I understand it, separately timed zones are suggested for floor areas exceeding 150m2. However, temperature control for separate living and sleeping areas is always required (usually using TRVs or subzoning) unless the flat is open plan and such control would be pointless.

Christian.

Reply to
Christian McArdle

Having by-pass valves with condensing boilers is not recommended and should be avoided. These raise the return temperature reducing efficiency. Try Grundfoss Alpha pumps.

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Reply to
Doctor Evil

Of course, many condensing boilers have internal pumps, so this advice can't be followed.

Christian.

Reply to
Christian McArdle

It can be I said "Having by-pass valves with condensing boilers is not recommended and should be avoided". Sound advice. There are many ways to get around this. A heat bank/thermal store. Replace the internal pump with a Grundfos Alpha. Install an intermediate buffer store - a 40 litre cylinder heated by the boiler, with a fixed speed pump between boiler and pump and Grundfoss Alpha between the rads and buffer cylinder, etc, etc.

The DIYers know all the answers don't they.

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Reply to
Doctor Evil

All these solutions are a bit OTT when you could just install the manufacturer's recommended auto bypass valve, assuming they haven't already incorporated one inside the case.

Are you seriously recommending:

a) Invalidating the warranty by replacing the internal pump. b) Spending hundreds of pounds (and lots of space) on completely unnecessary intermediate thermal transfer when you could just set the auto bypass high and not having it pass unless unnecessary?

You're really quite barking.

Christian.

Reply to
Christian McArdle

By-pass valves defeat the purpose of a condensing boiler, you have been told that

See makers first.

The intermediate also prevents boiler cycling too. Hundreds of pounds? For a small cylinder and stat?

You haven't a clue.

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Reply to
Doctor Evil

Yes, it began to sound a bit convoluted to me as well.

I've got my eye on the Grundfoss Alpha already, along with a Panda heat bank and a condensing oil boiler (open to suggestions) - there's no gas here. I've mentally returned the automatic by-pass valve for credit/adjustment for motorised valves.

Call me old fashioned, I understand the four-tapping arrangement with dedicated feed and vent pipe best, with 2-port valves for control. I prefer to fit my own pump.

But the bit I don't understand is the pump over-run. I know what it does, but there's no provision for that with the standard S-plan, is there? I've always wired the boiler and pump in parallel. I guess for boilers that need it there must be a special wiring arrangement from the boiler ?

Reply to
Jeff

From the building regs part L :

"1.39 In most dwellings one timing zone divided into two temperature control sub-zones would be appropriate. However in single-storey open-plan flats and bed-sitters, for example, sub-zoning of temperature control could be inappropriate. Reasonable provision in the case of large dwellings of more than 150m2 floor area, would be for no zone to have an area exceeding 150m2 and the operation of the heating to be separately timed in each zone."

Mind you most new houses are so small they probably don't count as large dwellings so you're probably right.

Reply to
Mike

Or an electronic sensing pump such as the Grundfos Alpha

Reply to
Mike

Building regs part L - see other post

Reply to
Mike

If they have internal pumps, wouldn't they also have internal bypass if needed ?

Reply to
Mike

You fit a pipe-stat somewhere convenient and arrange the wiring to keep the pump going until the water cools down a bit.

Reply to
Mike

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