Auto bypass valve not closing

[Hubcap]

I Have just had a new Worcester Greenstar 40CDi Conventional boiler fitted retaining the old Grundfos Super selectric 15-60 pump, set to 3.(P1W ;105). Three heating zones plus HW. The new bypass valve looks like a Honeywell DU145 but has a yellow, not red, knob. By feeling the temperature of the pipe, I can tell that the bypass is open, even when the system is starting from cold and TRVs are open. My question is, is this correct? I would have thought the bypass should only open when the heating circuit is closed by the TRVs. It is currently set to 6. I would welcome an expert opinion on this. Thanks in anticipation,
Hubcap

 

[SimonG]

Maybe just needs tweaking. Get the installer back.

 

[Hubcap]

Maybe just needs tweaking. Get the installer back.

Did that. He adjusted it from 2 to 6, but it's the valve is still open, i.e. the pipe is too hot to touch even when the TRVs are open.
What I'm really trying to find out is whether this is a fault so I can say so with conviction to the installer, if you see what I mean

 

[SimonG]

Sounds like it's faulty then.

 

[bob the plumber]

bypass return should only come hot when your 2 2 port valves shut and your pump overrun kicks in so there is something wrong. have you tried turning the pump down to 2 as it might be over working the bypass. other then that it sounds like it is sticking open and could do with replacing, shouldnt be to much of a job to do so

 

[Mbear]

This is why it's better to use a slightly opened gate valve as the bypass, there's nowt that can go wrong with them apart from leaking, but to be fair to gate valves any water component can leak

 

[doitmyself]

I Have just had a new Worcester Greenstar 40CDi Conventional boiler fitted retaining the old Grundfos Super selectric 15-60 pump, set to 3.(P1W ;105). Three heating zones plus HW.

Why such a large boiler? Did you or the installer use the Whole House Boiler Size Calculator to size it correctly or did you just assume that the previous boiler was the correct size? The output can be reduced by the installer if necessary.

The new bypass valve looks like a Honeywell DU145 but has a yellow, not red, knob. It is currently set to 6.

Then the ABV should be permanently closed!

How far from the ABV are you feeling the pipe? Heat can get transmitted through metal.

If your boiler is on max output, the ABV setting should be about 4 with your pump set to 3.

 

[Hubcap]

Why such a large boiler? Did you or the installer use the Whole House Boiler Size Calculator to size it correctly or did you just assume that the previous boiler was the correct size? The output can be reduced by the installer if necessary.


Then the ABV should be permanently closed!

How far from the ABV are you feeling the pipe? Heat can get transmitted through metal.

If your boiler is on max output, the ABV setting should be about 4 with your pump set to 3.

Reason for size of boiler: 20 Rads, detached house, single glazing. I'm feeling the pipe about a foot from the valve and it's same temp by feel as the output from the pump. Boiler is set to 5 on the knob on the front, pump is set to 3. Do you mean that the ABV should be permanently closed if it was working properly?
Thank you...

 

[AWheating]

the by pass should only open when its needed to maintain the min flow rate required by the boiler. it should be installed using the pumps manufactures charts in its instructions to determine the abv setting. the abv can be open/on at anytime the system needs it, this can be at anytime the system is running.

If your engineer has fitted and commissioned the abv correctly then it may be faulty and need replacing.

 

[AWheating]

http://www.google.co.uk/url?sa=t&rc...sg=AFQjCNE_zfkmMRf2H0en9-lBo-EyPUzU_Q&cad=rja

if you dont have the abv instructions.

 

[Hubcap]

Thank you AWheating. The link you gave is to the DU144, mine's the DU145 (albeit with yellow rather than red knob -don't know if the colour is significant), I have the instructions for the DU145 but the calculations are beyond a humble non-plumber like me. Would love to be able to work out what they mean though.

 

[AWheating]

i think the only difference is one is straight and one is angled.

 

[doitmyself]

Reason for size of boiler: 20 Rads, detached house, single glazing.

That points to a large boiler, but not necessarily a 30kW one. Use the link I gave to find out what you should have. The boiler output can then be reduced to the required value.

Do you mean that the ABV should be permanently closed if it was working properly?

No. I meant that, on a setting of 6 the pump would not be able to deliver enough pressure to open the valve.

As you can feel heat from the pipe after the valve with the valve on 6, there is a strong possibility that the valve is faulty. Have you checked that the valve is the correct way round (arrow on side points away from the pump)?

Assuming it is a Honeywell, the correct setting would be about 4.

Ask the installer the make of the valve.

 

[WHPES]

I've had this problem once and it was caused by a lump of solder jammed in the bypass valve preventing it from closing.