Suprima 70 - kettling?

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Bit of a long one this, but trying to cover everything:-

Suprima 70 (12-15 yrs old) in open system. Boiler fitted in garage.

Have had to reset boiler quite a few times recently and everything points to the PCB. Have just bought replacement, but before I fit it (and can't take it back for refund):-

Heating system has started banging (middle of night when no heating or hot water on). Presume this is because the frost stat is kicking in and starting the boiler up. Pretty sure it's kettling (hot water going back to F&E tank) as have had problem before but not for ages.

Banging lasts for 30 seconds or so then stops, then starts again after a few minutes. Interval between it restarting varies.

Had heating on all day for several days recently and no kettling and other than the resets it's been fine. Seems weird that it would only happen from frost stat although does coincide with the cold weather.

Green light on front panel flashing. Red light on - book says this is call to heat, but boiler has reached temperature, so not fired up.

Had heating guy round a day or so ago and he said pump working fine BUT at that time we weren't getting the kettling. He asked about kettling, but I said we hadn't had it for ages.

Boiler thermostat seems to be working fine as it shuts down when the stat is turned down.

Don't think it's a sludge problem as had radiator off recently and water clean. Although I do appreciate that this doesn't necessarily mean boiler/pump are clean.

Don't think it's an air lock as nothing has been changed or interfered with for ages (I know this isn't a guarantee).

Questions:

1 - Could it all be linked to the PCB, so it's worth fitting it?
2 - should I be replacing anything else at the same time - temperature sensor, overheat stat, etc?
3 - What else could it be?

Been awake for 2 hours since 2am with intermittent banging of pipes, so hope someone can help.
 
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All of your symptoms sound like a lack of flow.

Flow depends on pump operation. It could be sticking on startup. Turning the setting to "3" would increase the start torque. Did he do the "finger test" ?

A DIYer should not be changing the PCB as that involves opening the combustion chamber!

Tony
 

DP

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A DIYer should not be changing the PCB as that involves opening the combustion chamber!

What, on a Suprima?

Do agree end user better to get a pro in but many pros are worst than DIYers. Talk to friends and family for contact details of an operator they trust and rely on. A few good guys on this forum who will no doubt come to your aid OP.
 
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I doubt if a faulty PCB on the Suprimas would cause the banging, I think you have a wiring/pipe configuration fault, when the frost stat is activating is it also bringing the pump on as well as the boiler? and does the water have a route to follow i.e. if both zone valves are closed (S plan) is there a by pass for the water to flow back to the boiler if its a Y plan is the pump running when frost stat operates
 
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Agile - I dare not ask but what's the finger test. I think he turned the pump up. It's on 3 already I know the engineer took the front screw out - Grundfos pump

Replacing the PCB looks straighforward enough on this model

Lanmcd - yes the pump comes on when the frost stat operates. Not sure what the configuration is for definite, but think its S plan with a small circuit taking water to the boiler. The system itself is all over the place though thanks to successive additions for extensions by various engineers. On some of the CH system we get hot radiators when only the hot water is on!

Banging now occurring when heating and hot water on.

Will call engineer. He's pretty good and very helpful. Just didn't want to disturb him over the weekend!

Thanks for the help guys.
 
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It's not the pcb, the water is not being got rid of fast enough for the heat that is being produced by the boiler, either lower the boiler thermostat, or the pipework is getting either scaled up or coated with sludge in the primary flow and return pipes. they almost certainly need descaling and desludging, there may also be a build up inside the heat exchanger. All these things slow down the rate at which water can move, slow the pump speed down it gets worse, speed it up it gets a bit better, but not for long.
 
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Appreciate what you have said Peter and will look into this, but it only seems to be happening with the frost stat not the heating and water. I'll call my engineer out tomorrow.
If someone has the patience can you explain for my benefit how the frost stat works? I know what it does but where does it draw the water from to feed the boiler and where does the heated water go?
 
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The frost stat is fitted on the return pipe near the boiler or in the loft. it is set tom switch on, closed circuit when temperature of pipe drops below about 5 degrees centigrade. It switches the boiler on and if the motorised valves are 2 then there is a bypass loop between the hot water flow and the heating flow so that the water heated by the boiler can go back to the boiler. If it is a single 3 port valve then the bypass should still be used but when valve is closed the hot water is open so the boiler will heat the hot water until the return pipe temp goes above 5 degrees cent or whatever it is set at. The frost stat switches the pump and boiler on regardless of what the other controls are saying, if it is wired correctly, and if it is working properly since they do fail like everything else, since we live in a world where most things are now made and designed with a built in obsolescence.
 
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Thanks Peter

Think I've found the bypass loop - for some reason the (manual) valve was closed. I've opened it and hope it does the trick. So far, so good. Let's see if I get a good night's sleep :)
 
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