Grudfos Alpha & Potterton Suprima 'bug'?

[Rory]

I installed an Alpha during the summer and, now the CH is on, I've noticed that whenever the Suprima re-fires after the boiler stat has shut it down, then the Alpha speeds up before gradually settling down again. This means that, contrary to the way it's supposed to work, the noise through our TRV's is quite loud, and all the more noticeable because it comes & goes. The Alpha is set at the lowest point on its variable scale. I *think* that what's happening is that the Suprima is momentarily disconnecting the pump as the boiler fires? If this is true, then the pump is acting correctly. Is this (disconnecting the pump) a known *bug* with the Suprima? Thanks Rory

[raden]

In message , Rory writes

When a Suprima comes on, it momentarily energises the pump, this is normal. It should also energise the pump on a daily basis to prevent it seizing up during the summer

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[IMM]

It is best to have the pump externally controlled, so that when the boiler pulses the pump it really doesn't matter as it is running anyhow. Also when the CH it on it is best to have the pump running continuously and allow the boilers burner to cut in and out.

[Rory]

Thanks for both replies - energising the pump is fine, it's the momentary drop-out before energisation that appears to cause the problem (of the pump speeding up).

IMM's suggestion accords with my own thinking - I believe I could achieve this by simply shorting Switched Live and Pump Live on the boiler (so the pump will run if the valves are open but will still over-run too). Is there any reason not to do this - might it upset the boiler controller?

[IMM]

I can't see any reason why it would. The boiler would switch the pump when needed. If the pump is not running then it switches, if running, it doesn't care. The temperature in the house will be a little more stable with the pump running all the time when on CH.

[Rory]

Drat - it's not so easy. The controller sees this as a wiring fault and puts the boiler into lock-out. Now I look, this condition is in the Fault Finding Guide.

[IMM]

Put a relay in. The boiler energises a relay which switches the pump. Isolate the backfeed from the external switching from the pcb. A relay for £3 and base £2 from Maplin.

[raden]

In message , IMM writes

You keep your CH on all through the summer ?

or did you not read what I typed ?

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[Rory]

That would work as long as the controllers not doing anything super-clever. Strange that it monitors the pump live at all, really, because it can only go live under the boilers control. Perhaps I could break the track on the PCB that provides the f/b!

[Rory]

Actually, I can't see that a relay would help - presumeably the coil would be wired to pump live, so it would still pulse the pump as the boiler fires. If I connect another live to the pump somewhere then either the pump or boiler would run 24/7 and/or the boiler would still see it as a wiring fault.

[IMM]

Ask Maxie about that. I would prefer a simple cheap relay.

[IMM]

Maxie, will reveal if it actually "pulses" the pump. What length a pulse is, is open to interpretation.

[raden]

Send it to yourself via Securicor and let them do it for you !!!

Modifying the pcb in your boiler is not a good idea, you leave yourself open to all sorts of problems, legally for a start.

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[IMM]

Read other post on this...inserting a relay.

[Rory]

On the Suprima surely the pump running every 24hrs in the summer

*generally* doesn't matter as it can only be used on fully pumped systems?

[Rory]

I reckon what I need is a relay with a time delay off (for the overrun) with the coil wired to the boilers Switched Live (ie the input from the valve microswitches). If I wire the pump to the relay's common, it's n/o to a permanent Live and its n/c to the Pump Live then it should works as desired. The only thing that concerns me slightly is that in the boilers fault Finding Guide it suugests *intermittant* lockout can be caused by Pump Live and Switched Live being connected - when I did it, it locked out straight away.

[IMM]

The relay isolates the external pump live. Or you could forget switching the pump from the boiler pcb altogether. Use a pipe stat on the flow very near the boiler. This switches the pump. When the flow is above say 65C the pump keeps running until the boiler cools. Not only that you have control via the pipe stat on the level of heat to be removed from the boiler. This is more specific, rather than just a timer, which may over-pump and over-cool the boiler. Simple and Sorted!

[Rory]

Thanks for your ideas - I'm slightly baffled as to how the pipe stat would be wired to the pump. I can see how it would stop the pump as the flow temp dropped below (say) 65C, but how do I get the pump to start when the system is cold and the stat contacts would be open? I can't connect Live to Pump Live in any way (as the boiler sees it as a fault). The only solution I can think of is to wire Pump Live to a relay coil and then have the n/o contacts in parallel with pipe stat. Is there a simpler way (without a relay) that I'm missing?

[Tony Bryer]

The pipe stat will have n/o and n/c contacts. Common goes to pump, n/c to boiler call, n/o to permanent live. Boiler switches on and pump runs. When the set temp is reached the stat switches over and the pump keeps running until the system cools down.

[Rory]

Thanks - I can see that would work. However, the original problem is that the boiler restarts my Alpha pump every time it fires (so it speeds up for a while before settling down again). This (the restarting) would still happen as the pipe stat contacts changed over (although I appreciate it would be much less frequent than it is now). I'm minded to try the delayed off relay approach - at least I can contain that in the boiler cupboard, a pipe stat would have to be external.