I need to sort out the rad balancing for my CH system (open vented
S-plan, with TRV4s on all but one rads) and have come across this
Drayton document:

https://www.ukplumbersforums.co.uk/a...trv-pdf.37662/

In step 3 para 6 it refers to "Gradually open the primary flow to the
hot water cylinder again". This implies that there should be some sort
of flow control valve fitted to the HW circuit, which my system has
never had, so when HW is called for a lot of the flow will be passing
through this loop. Could this be why my boiler sometimes trips out
with an overheat error?

If needed what sort of flow control vavle would be best to fit (I need
to drain the system anyway for some other maintenance work that needs
doing).

On Sat, 16 Mar 2019 14:15:31 +0000, Davidm wrote:

In step 3 para 6 it refers to "Gradually open the primary flow to the
hot water cylinder again". This implies that there should be some sort
of flow control valve fitted to the HW circuit, which my system has
never had, so when HW is called for a lot of the flow will be passing
through this loop.
Could this be why my boiler sometimes trips out with an overheat error?

No, you dont need a flow control valve. You should have a bypass valve,
or, one of the radiators without any TRV control.
Thats so if all radiators have reached their set temperature, the TRV
shuts, stopping flow through that raditor. If all rads have TRVs, and all
are shut, there is nowhere to go for the heat output from the boiler.

The boiler will only come up with an overheat fault if there isnt enough
flow to keep the heat exchanger output below the recommended temperature
(70 degrees?), or, there is a fault with the boiler, or a restriction
somewhere.

On 16/03/2019 15:09, Alan wrote:
On Sat, 16 Mar 2019 14:15:31 +0000, Davidm wrote:

In step 3 para 6 it refers to "Gradually open the primary flow to the
hot water cylinder again". This implies that there should be some sort
of flow control valve fitted to the HW circuit, which my system has
never had, so when HW is called for a lot of the flow will be passing
through this loop.
Could this be why my boiler sometimes trips out with an overheat error?

No, you dont need a flow control valve. You should have a bypass valve,
or, one of the radiators without any TRV control.
Thats so if all radiators have reached their set temperature, the TRV
shuts, stopping flow through that raditor. If all rads have TRVs, and all
are shut, there is nowhere to go for the heat output from the boiler.

The boiler will only come up with an overheat fault if there isnt enough
flow to keep the heat exchanger output below the recommended temperature
(70 degrees?), or, there is a fault with the boiler, or a restriction
somewhere.


So maybe the overheat error occurs when all the TRVs are closed. I have
always thought that a programmable thermostat was a better arrangement.

--
Michael Chare

On Sat, 16 Mar 2019 10:09:27 -0500, Alan wrote:

On Sat, 16 Mar 2019 14:15:31 +0000, Davidm wrote:

In step 3 para 6 it refers to "Gradually open the primary flow to the
hot water cylinder again". This implies that there should be some sort
of flow control valve fitted to the HW circuit, which my system has
never had, so when HW is called for a lot of the flow will be passing
through this loop.
Could this be why my boiler sometimes trips out with an overheat error?

No, you dont need a flow control valve. You should have a bypass valve,
or, one of the radiators without any TRV control.
Thats so if all radiators have reached their set temperature, the TRV
shuts, stopping flow through that raditor. If all rads have TRVs, and all
are shut, there is nowhere to go for the heat output from the boiler.

The boiler will only come up with an overheat fault if there isnt enough
flow to keep the heat exchanger output below the recommended temperature
(70 degrees?), or, there is a fault with the boiler, or a restriction
somewhere.
As I said in para 1 of my OP (which isn't in your reply) I have one
rad with no TRV for this very reason. I also have an auto bypass
valve, one side connected before the two (CH and HW) zone valves and
the other side to the boiler return.

So why don't I need to control the flow in the HW circuit, and balance
that out with the flow in the CH side?

On Sat, 16 Mar 2019 15:44:00 +0000, Michael Chare wrote:

On 16/03/2019 15:09, Alan wrote:
On Sat, 16 Mar 2019 14:15:31 +0000, Davidm wrote:

In step 3 para 6 it refers to "Gradually open the primary flow to the
hot water cylinder again". This implies that there should be some sort
of flow control valve fitted to the HW circuit, which my system has
never had, so when HW is called for a lot of the flow will be passing
through this loop.
Could this be why my boiler sometimes trips out with an overheat
error?

No, you dont need a flow control valve. You should have a bypass valve,
or, one of the radiators without any TRV control.
Thats so if all radiators have reached their set temperature, the TRV
shuts, stopping flow through that raditor. If all rads have TRVs, and
all are shut, there is nowhere to go for the heat output from the
boiler.

The boiler will only come up with an overheat fault if there isnt
enough flow to keep the heat exchanger output below the recommended
temperature (70 degrees?), or, there is a fault with the boiler, or a
restriction somewhere.


So maybe the overheat error occurs when all the TRVs are closed. I have
always thought that a programmable thermostat was a better arrangement.

Better than what?
You fit the stat in the coldest room, usually the hallway which also has
the rad without the TRV.

On Sat, 16 Mar 2019 15:44:00 +0000, Michael Chare
wrote:

On 16/03/2019 15:09, Alan wrote:
On Sat, 16 Mar 2019 14:15:31 +0000, Davidm wrote:

In step 3 para 6 it refers to "Gradually open the primary flow to the
hot water cylinder again". This implies that there should be some sort
of flow control valve fitted to the HW circuit, which my system has
never had, so when HW is called for a lot of the flow will be passing
through this loop.
Could this be why my boiler sometimes trips out with an overheat error?

No, you dont need a flow control valve. You should have a bypass valve,
or, one of the radiators without any TRV control.
Thats so if all radiators have reached their set temperature, the TRV
shuts, stopping flow through that raditor. If all rads have TRVs, and all
are shut, there is nowhere to go for the heat output from the boiler.

The boiler will only come up with an overheat fault if there isnt enough
flow to keep the heat exchanger output below the recommended temperature
(70 degrees?), or, there is a fault with the boiler, or a restriction
somewhere.


So maybe the overheat error occurs when all the TRVs are closed. I have
always thought that a programmable thermostat was a better arrangement.
I have a progammable thermostat, and one rad with no TRV (see my
original post).

On Sat, 16 Mar 2019 16:41:54 +0000, Davidm wrote:

As I said in para 1 of my OP (which isn't in your reply) I have one rad
with no TRV for this very reason. I also have an auto bypass valve, one
side connected before the two (CH and HW) zone valves and the other side
to the boiler return.

So why don't I need to control the flow in the HW circuit, and balance
that out with the flow in the CH side?

It is an S plan, the HW flow will stop once the hot water is at the
correct temperature.
Balancing is to get the radiators to all achieve the same temperature,
or, adjust them if you want one hotter than the others. It is done to
make sure that the first radiator(s) in line do not take all the heat.