Automatic Bypass Valve on 15mm pipe - is this correct

BTC · 17 Dec 2010

I've got a recent S-Plan system (less than 4 years old) that has TRVs fitted to some of the rads. I want to go to an all TRV system.

Looking at the pipes, I've noticed what looks to be an automatic bypass between the primary after the pump but before the split and two motorised valves.

It passes through what to my unskilled eyes looks to be an automatic valve and then back to the primary return. It's in 15mm pipe.

Two questions:-

Am I going to run into problems if I put TRVs on all the radiators? I thought that by-passes needed to be 22mm?

Secondly, could this 15mm pipework and valve be the source of a noisy few minutes after system shutdown? Would a 22mm bypass cure this, or are the by-pass valves inherently noisy?

Christmas cheers in advance!

D_Hailsham · 17 Dec 2010

BTC said:
I want to go to an all TRV system.

But not on the rad which is near the wall thermostat.

I've noticed what looks to be an automatic bypass

Post a pic.

It's in 15mm pipe.

Depends on what the boiler manufacturer specifies. Which make/exact model boiler do you have?

Secondly, could this 15mm pipework and valve be the source of a noisy few minutes after system shutdown? Would a 22mm bypass cure this, or are the by-pass valves inherently noisy?

What sort of noise is it and where does it appear to come from or be the loudest?
How long does the noise last?

BTC · 17 Dec 2010

Thanks for the response

D_Hailsham said:
But not on the rad which is near the wall thermostat.

I'm going for a home automation system with zone control via motorised TRVs, so there'll be no single wall thermostat - hence why I need all TRVs.

Post a pic.

Fumbling for my camera now!

Depends on what the boiler manufacturer specifies. Which make/exact model boiler do you have?

British Gas 330 which I believe is a rebadged Glowworm - I think a 30 hxi.

What sort of noise is it and where does it appear to come from or be the loudest?
How long does the noise last?

The noise is a loud whirring/whistling noise that comes from the area of the pump/valves and what I think is the by-pass valve (they are all within a foot of each other in the loft). It lasts up to 10 minutes after shut down and rises gradually in pitch. It is much noisier than the usual running noise you get from the system.

D_Hailsham · 17 Dec 2010

BTC said:
I'm going for a home automation system with zone control via motorised TRVs, so there'll be no single wall thermostat - hence why I need all TRVs.

How will the system provide a boiler interlock, i.e turns the boiler off when rooms are up to temperature?

Post a pic.

Fumbling for my camera now!

British Gas 330 which I believe is a rebadged Glowworm - I think a 30 hxi.

That's a large boiler for the typical domestic property. Do you have a very large uninsulated house?

The noise is a loud whirring/whistling noise that comes from the area of the pump/valves and what I think is the by-pass valve (they are all within a foot of each other in the loft). It lasts up to 10 minutes after shut down and rises gradually in pitch. It is much noisier than the usual running noise you get from the system.

The boiler has a pump overrun, which keeps the pump running for several minutes after the boiler goes off. You can probably hear the water passing back to the boiler through the bypass valve. The rise in pitch is probably due to the valve slowly closing. It shouldn't make this noise.

How was the size of the boiler determined?

BTC · 17 Dec 2010

D_Hailsham said:
How will the system provide a boiler interlock, i.e turns the boiler off when rooms are up to temperature?

The zone thermostats and motorised rad valves communicate wirelessly. The system has a wireless relay device that replaces your old roomstat. The device listens to the wireless traffic to see if any of the zones are demanding heating and calls for heat accordingly. All jolly clever stuff.

More details here:

Relay
Zone thermostat and TRV actuator

That's a large boiler for the typical domestic property. Do you have a very large uninsulated house?

4 bed 2 bath dorma bungalow with 1970s vintage dorma conversion. Most of the radiators are old and under spec according to a radcalc.co.uk. I'm currently getting quotes to get them replaced. It's been hard to heat some rooms during this cold snap!

The boiler has a pump overrun, which keeps the pump running for several minutes after the boiler goes off. You can probably hear the water passing back to the boiler through the bypass valve. The rise in pitch is probably due to the valve slowly closing. It shouldn't make this noise.

How was the size of the boiler determined?

By BG who fitted the system.

Thanks for your help so far here's a pic of what I think is this bypass valve:

Automatic bypass valve?

BTC
17 Dec 2010
1

Poor lighting unfortunately.

tamz · 18 Dec 2010

Must admit i have never seen this type of valve before in near 40 years It is not however, an automatic valve of any kind. It is manual. It has a flow guage to register the flow through the bypass and a screw valve for adjustment.
The noise on shut down will be caused by insufficient flow through this valve (it is nearly shut).
Fit a new automatic valve when you change the valves and yes they are 22mm.

Mr Hailsham
You need to keep on top of new developments. Lots of new reading out there

D_Hailsham · 18 Dec 2010

BTC said:
D_Hailsham said:

How was the size of the boiler determined?

Click to expand...

By BG who fitted the system.

If the rads are undersized, it doesn't matter how big the boiler is - the house will never get warm.

Use Boiler Size Calculator to find out what size boiler you should have.

BTC · 18 Dec 2010

The noise on shut down will be caused by insufficient flow through this valve (it is nearly shut).

I'm guessing that the rising pitch will be because the system pressure is going up as the pump works against the valve?

I've had a better look at the valve body now, and it's a Taconova Setter valve. It's set to the right-hand "B", whatever that means. I googled it: specs here

I'll have my plumber take a look at it when I get the rads replaced and see if he can fit an automatic valve in its place in 22mm pipe.

Regarding the boiler, a (rough as I'm not going to measure the exact house sizes) calculation says 13kW. According to the BG site the boiler is dial-an-output from 9.3 to 30kW. I now vaguely remember them telling me this when they fitted it, and that they had set it up to what they thought the house needed.

Thanks for the responses.

D_Hailsham · 18 Dec 2010

BTC said:
Regarding the boiler, a (rough as I'm not going to measure the exact house sizes) calculation says 13kW. According to the BG site the boiler is dial-an-output from 9.3 to 30kW. I now vaguely remember them telling me this when they fitted it, and that they had set it up to what they thought the house needed.

If you only need 13kW, why install a 30kW. As you say the 330 will modulate down to 9.3kW, but that only allows the outside temperature to rise to about 5°C before the boiler starts cycling.

An 18kW boiler, which modulates down to 6kW, would have been much more sensible as it provides cover down to -9°C (given large enough rads) and up to 11°C.

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Automatic Bypass Valve on 15mm pipe - is this correct

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