Auto pressure release valve - where to fit?

russella · 13 May 2010

Hello all,

I'm fitting TRVs to my radiators (see layout below), if I turn all the TRVs off I get a fairly unpleasant noise coming from the boiler and I've been advised that a auto pressure release valve would be a good solution? Is this right, and if so where should I fit it?

The pipework from the boiler and feeding the downstairs radiators is 22mm, the pipwork upstairs is all 15mm. The boiler's a Baxi Duotec 28.

Untitled

russella
13 May 2010
1

Thanks,

Russ

Happyplumber · 13 May 2010

ITs not auto air vent ,its automatic bypass valve you need fitted
.

Normally one radiator usaully the bathroom has normal lockshield valves,so act as bypass

Bypass is there to protect the boiler and its heat exchanger from damage

Agile · 13 May 2010

You need an auto bypass valve.

It needs to be fitted across the circuit after the pump and before the motor valves ( if any ).

Tony

russella · 13 May 2010

Thanks for the replies so far.

I've not got any motorised valves fitted, how far from the pump should it be fitted? I think I remember reading before it should be fitted a certain distance from the boiler, something to do with the temperature of the water returning to the boiler?

Russ

hammerswinger · 13 May 2010

The Baxi Duotec has a built in automatic bypass....

From the installation instructions:

"The boiler utilises the primary side of the DHW plate heat
exchanger as an automatic integral bypass"

Cheers.

russella · 13 May 2010

hammerswinger said:
The Baxi Duotec has a built in automatic bypass.

Thanks Hammerswinger, I must admit, I was under the impression these built in valves were a bit naff? But at the same time I have to say I'm hardly a plumber! Just a diy-er with a lot of google-time on my hands.

hammerswinger · 13 May 2010

I don't know if the built in bypass is any good or not.
Having a rad as a bypass would be better than relying on a valve in my opinion. I don't suppose fitting an additional bypass valve would hurt.

The rad closest to the room stat shouldn't have a TRV fitted anyway.

Cheers.

Agile · 14 May 2010

Most of the bypass valves inside boilers are designed to protect the boiler and so most of the boiler instructions still ask for an external one or similar arrangement.

That boiler method seems seriously liable to scale up the plate! It may be adjustable and might not be best set.

Tony

hammerswinger · 14 May 2010

Can't see anything in the instructions that refers to adjusting the automatic built in bypass, there's also no mention of having to fit one externally either.

They're probably relying on not all rads having TRV's.

Cheers.

PEDANTICVINDICTIVEMAN · 14 May 2010

Isn't this going to conflict with Part L regarding the interlock, if the TRV's shut down, the room stat aint reach temp and aint gonna click off the boiler, the boiler will keep cycling, anti Part L, take off the trv on the rad that the room stat is in, this will be your byepass and stop the boiler making a noise.
Dont tell me you aint got a room stat.

doitall · 14 May 2010

PEDANTICVINDICTIVEMAN said:
Isn't this going to conflict with Part L regarding the interlock, if the TRV's shut down, the room stat aint reach temp and aint gonna click off the boiler, the boiler will keep cycling, anti Part L, take off the trv on the rad that the room stat is in, this will be your byepass and stop the boiler making a noise.
Dont tell me you aint got a room stat.

PVM, long time no see, where ya been hiding man.

Trust you're fit and well.

russella · 14 May 2010

PEDANTICVINDICTIVEMAN said:
Dont tell me you aint got a room stat.

Actually, it's a little more complicated than that - we're using a system called Homeheat (or IQ3), where each room or zone has its own thermostat, that controls one or more mechanical TRV heads. So we can control the temperature in each zone and the times that the zone is on.

The system can also control the boiler based on whether or not any zones need heat, but we've not got that installed yet!

Russ.

doitall · 14 May 2010

Take a couple of heads off until you get it fully installed then.

I would still cut an AVDO auto by-pass into the circuit, just to reduce the pump noise, if nothing else.

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Auto pressure release valve - where to fit?

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