BS 6700 questin.

[Nordio]

5.3.5.6.1Vented primary circuits
Vented primary circuits shall have a vent route connecting the flow connection on the boiler to the vent pipe outlet above the expansion cistern and a feed water route from a point near the bottom of the expansion cistern to the return connection on theboiler.
Except as specified in this subclause, these routes shall be independent. It is permissible for both these routes to be incorporated in parts of the primary flow and return pipework, but the vent route shall not include any valve, pump or any impediment to flow whatsoever.
Where the design of the primary circuit so dictates, it is permissible to include a circulating pump and its associated isolating valves in the feed water route. A feed and expansion cistern for a double feed primary circuit shall accommodate 4% expansion of the volume of the water inthe circuit. Except for a circulating pump and its associated isolating valves and except for a servicing valve, both fitted only in the circumstances specified in this sub clause, the feed water route shall not include any valve, pump or any impediment to flow what so ever. Where the vent route and water route are combined, the boiler and primary circuit shall have the protection specified in 5.4.

Does the part highlighted in bold mean its ok to have a circulating pump in the feed water route?
Its a solid fuel system and I want to stay within the regs but intrepeting these are a bit confusing.
Can anyone shed any light on the subject?
Thanks.

 

[Ged Simpson]

It implicitly states that it is permissible to have a circulating pump and its associated valves in the feed water route, but only the circulating pump and its associated isolation valves. So yes you can, just make sure the rest is unobstructed pipewok.

 

[Nordio]

Ok thanks.

I have a copy of CIBSE's "Domestic Heating Design Guide" and it states on page 71 that the F&E pipe must not have any valve fitted on it.

It goes on to say.........

An important function of the feed and expansion pipe is to quickly replenish water in the system to protect the boiler in the event of the operating thermostat failing in the open position. This will allow the burner to continue to function and generate steam, which would escape to atmosphere along the open safety pipe.
For this reason, it is important that there are no restrictions such as motorised valves or manual valves along the route the feed water will take to the boiler.

Also I have a copy of Oftec's "Domestic Heating Systems" (Technical book Four) which states in section 2:2:1..........

The feed and expansion pipe must be able to keep the boiler full of water no matter what happens to any valves or controls fitted to the system. Therefore no valves are permitted to be fitted within the feed and expansion pipework.

 

[Ged Simpson]

if your feed pipe and vent are not independent, then the pump cannot be incorporated in that section. If the vent pipe and the feed pipe are independent, the pump may be incorporated in the feed line. Ideally, the pump should be in the flow line with the vent connection teeing in on the suction side of the pump and independent of the feed line which should tee into the return line to the boiler.

 

[diamondgas]

If I may put my thoughts here ... I've always looked at the dangers of fitting any kind of isolation or restriction on the open vent pipe from an uncontroled sorce of heat as a no-no! If the pump and its iso's in anyway restrict boiling water expaning up the vent and out, then it has do be potentially dangerous! ... Tee the vent before the pump take off ... IMO!

 

[kirkgas]

If I may put my thoughts here ... I've always looked at the dangers of fitting any kind of isolation or restriction on the open vent pipe from an uncontroled sorce of heat as a no-no! If the pump and its iso's in anyway restrict boiling water expaning up the vent and out, then it has do be potentially dangerous! ... Tee the vent before the pump take off ... IMO!

you are correct you dont have anything on the vent dection, what BS6700 says is that it is permissible to have it on the feed section (although it isnt best practice), by definition when you have the cold feed dropping down and tee'ing into the circuit under the floor it could be near the pump so it is ineffect on the same circuit, but as i say you must have a clear, unobstructed path and as short and direct route as possible from the burny bit to the tank so that when the boiler overheats the water it can fire straight up the vent to safety

 

[doitmyself]

5.3.5.6.1Vented primary circuits
Vented primary circuits shall have a vent route connecting the flow connection on the boiler to the vent pipe outlet above the expansion cistern and a feed water route from a point near the bottom of the expansion cistern to the return connection on the boiler.

So what has happened to the 150mm between feed and vent?

Having the feed and vent on opposite sides of the boiler was OK when the heat exchanger was cast iron and the pressure drop through the Hex was minimal. But with modern high pressure drop Hex's, following the above advice is a recipe for disaster.

 

[peteheat]

On solid fuel stoves and wrap around back boilers we always fitted the pump on the return, the reason was to prevent "tipping" or overflow from the vent pipe, in our old tin pot way we relied on gravity to heat the rads and cylinder upstairs and the pump was mainly for the ground floor circuit and to pump the heat around the system faster.

That said I doubt a pump is classed as a valve as the hot water can expand to safety through it.

 

[Nordio]

On solid fuel stoves and wrap around back boilers we always fitted the pump on the return

Blocking the feed route? That doesn't seem like convention with a solid fuel boiler.

Where the design of the primary circuit so dictates, it is permissible to include a circulating pump and its associated isolating valves in the feed water route.

Using the above quote from the regs, did the design of your primary circuit thus dictate?
In other words were you adhering to the MI's (Manufacturer Instructions) or were you taking a short cut?

 

[peteheat]

Hi Nordio,

No blockage the system can still feed through the pump, I have seen systems where the feed from the F&E was connected to the expansion, now that one I didn't agree with.

We always come off the stoves and back boilers in 1" copper, depending on the run and stove output we might leave it in 1" all the way to the F&E though most times we could drop to 3/4 above the cylinder.

Sorry forgot the site is mainly UK, 1" = 28mm 3/4" = 22mm, one of those Irish things supposed to be good Europeans but we hold imperial measurements for our pipes and fittings while the UK moves to metric 🙂

 

[peteheat]

Hi,

Point to clarify the above as DIY'ers may read this thread along with
this one



As can be seen from the attached image the expansion pipe should be installed without restriction to vent above the F&E tank.

In two story installations we tee off the rising flow and return to serve the upstairs circuit.

In many houses we could not take the flow and return off the other side of the appliance in which case we would tee off (drop down) the flow just past the safety valve and the same on the return.

The pump was fitted on the return from the ground floor level and activated by a pipe stat on the flow.

When installing in bungalows it is necessary to raise the cylinder off the floor by at least 600mm (2 feet in old money) the purpose is to have the gravity flow rising to the top coil in the cylinder.

When linking systems we recommend a dual coil cylinder to allow the solid fuel appliance circulate unrestricted, the second appliance (Gas or Oil) can be plumbed using the second coil and have a two port valve fitted as per standard S plan.

The heat output of the solid fuel appliance dictates the next modifications, some can have boilers with an output as low as 4Kw in which case a heat dump radiator and the cylinder should be sufficient for safe operation.

As to the quality of South of Ireland plumbing I am aware there are plenty of questionable installations, that said I have come across some in the UK and N.I. that make the worst Irish installations look lke works of art, there are cowboys and over confident DIY'ers everywhere.

We have sold one Olymberyl stove mentioned in that thread and do not sell them anymore, they are not a bad stove for their price range, my problem with them is on a technicality.

One thing I can confirm is they should never be installed as part of a sealed system, they are solid fuel which means no control in the event of a power or pump failure.