potterson gas boiler,flow issue bypass valve

jj58 · 24-11-2013 10:59pm #1

okay,potterson gas boiler in new part of house(extension)
extension is heating perfect as there is 4 rads on it, old part is 10mm microbore hottest i can get the top of the rads is 50-55 deg when boiler is turned up to 80deg (bottom 35-40)
i have flushed/pre treated system.
there is also a 5m circ pump on the return manifold from the microbore.
what is happening is boiler has flow temp of 78 deg and return back from the rads of 44 max
but when i check temp at return from bypass valve i get 68 deg

i think there is too much going through the bypass valve of boiler and not to the rads
,
solution maybe? there is a second pump on the zoned microbore manifold(11 rads single) is on the return putting positive pressure on the bypass valve.( even without pump turn on i get bad results)
if i transfer pump to the flow pipe of manifold, will it put negative pressure on the bypass valve?? and thus the heat from the boiler will go to the rads instead of through the bypass valve again.

rang potterson , they had no clue,

so the rads dont heat up cause the boiler modulates because of the return temp is high from the bypass valve.
what im saying is, will my idea work,??
any other soultions??

shane0007 · 24-11-2013 11:08pm

First off turn off the bypass valve. Boiler modulation will not be an issue but if the boiler has a modulating circulating pump, this can be of issue. This will depend on what model boiler you have & whether you can force the pump not to modulate.

Microbore will always be a pain in the backside. The small bore surface area creates enormous resistance & thus circulation will go through lesser resistive routes.
Is the microbore manifold a pipe manifold or a manifold box?
Have you done a mechanical powerflush of the system?
Can you isolate all other circuits including the cylinder to force flow through the microbore circuit?

jj58 · 24-11-2013 11:40pm

proper power flush chemical power flush unit.kamco cf 30
its a potterson promax HE. or something like that, LPG.
how do you turn off the in built bypassd valve
rang potterson twice, 2 diff bucks, gave me no help what so ever, just said nothing i could do.
its a 1" pipe manifold, all single rads, small thin type too. little water content, when power flushing got em hot.

shane0007 · 24-11-2013 11:51pm

Sorry I thought you were talking about an external bypass.
That boiler cannot force high speed.
You obviously have a blockage for that much low temperature to the rads. Boiler is just cycling through its own circuit. Are you getting full proper temps on other circuits such as cylinder coil?

shane0007 · 24-11-2013 11:57pm

Can you shut down all other circuits?

jj58 · 25-11-2013 12:00am

I have shut of all circuit still no better.
even with 4 or 5 rads on the output is poor

shane0007 · 25-11-2013 12:02am

Do all other circuits heat as they should?

jj58 · 25-11-2013 12:15am

yes but here are little rads on the circuit and very near the boiler,
i have clamped on my thermeters from my fluegas analyser and i think there is too much going through the bypass valve, thats why i think transferring the pump from return on the manifold to the flow will put less pressure on the bypass valve, i could be wrong, looking for second opinion

shane0007 · 25-11-2013 12:20am

No it won't be a boiler issue. The internal bypass in those are tiny. That's why an external bypass should always be fitted when fitted on fully zoned systems.

The issue is pipework on that circuit. Did you dismantle the manifold? You could fit a temporary link between the flow & return at the manifold & see if that heats as it should. Then you would know for sure the issue is beyond that point.

esox28 · 25-11-2013 12:31am

I'm I right in thinking you have a second circ. Pump on the microbore zone separate to the boilers pump?

jj58 · 25-11-2013 8:49am

yes there is a second pump on the microbore system, comes on when u turn on that zone,
i have tested with or without the pump been turned on.
shane had a good idea to loop/ link the manifolds,
either way it may not be a solution

shane0007 · 25-11-2013 11:10am

TBH, the issue is going to be the microbire network. If you cannot achieve an acceptable flow rate through it, the ultimate option will be narrowed to re-piping it in small bore.

esox28 · 25-11-2013 8:11pm

Would it be possible that zone pumps output maybe in question and being in place is just creating too much resistance for the boilers circ pump to over-come.

JohnnieK · 25-11-2013 11:57pm

I would be looking at a restriction too. Under normal operation the boiler pump is hitting a brick wall.

I would put the link in between the flow and return just to be certain.

Feckin micro-bore.:mad:

jj58 · 11-12-2013 8:22am

just letin ye know i fixed that problem
i put the pump on the flow pulling from the boiller.
which had a negative pull on the bypass valve, worked absolute perfect.
i always knew there was too much going through bypass, too high of temp returning because of that, which caused boiler to modulate.
and the heat in the rads never improved
with nothing going through the bypass cause of a pull on the bypass the boiler didnt modulate too early.
theres one for ya
cheers

11-12-2013 10:29am

Anytime a secondary pump is added to a gas boiler installation there is the possibility of funky faults as the extra pump can cause problems, it can change the characteristics of the boiler as the boiler hasn't been designed with that pump in mind.

potterson gas boiler,flow issue bypass valve

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