Baxi Bermuda Pump underrun

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IamTheClueless1

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The problem is that the pump appears to shut down before the boiler switches down. This causes the boiler to \\\'boil\\\' the water, with the resultant hysterical popping and banging in the boiler and surrounding pipework which resonates around the house. My 20 month old daughter is frequently awoken in the night and creates nearly as much noise as the boiler.

Is the pump failing, or is there some sort of \\\'switching\\\' on the boiler which is at fault, shutting the pump off too soon?

Please help we could all use some sleep :)
 
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How old is the boiler? How long has it been doing this?

Do you live in a hard-water area, and how much limescale to you get in your kettle? (this is not a joke)
 
the age of the boiler is unknown but i expect it is around 40 years old, the same age of the house. The house had been unoccupied for around a year before we recently moved in, and several radiators had leaking valves which i replaced.

As i had already drained the system down, i refilled it with a propriety cleanser/descaler which is still in the system as recommended by the product info. The area has very hard water, and the kettle needs regular descaling. I have also fitted a 'waterking' electronic scale inhibitor to the mains supply.

the heating works fine whilst the pump is running until it shuts down a few minutes before the boiler, then the 'kettling' starts - i imagine this is because the circulation has stopped.

I have varied the thermostat setting on the boiler with marginal success, i.e. the lower the setting the less the noise.

thanks for the reply
 
I presume your hot water is gravity not pumped, and the boiler takes itself up to temperature so it can circulate to the cylinder. Does this mean there is not a cylinder electric stat, but perhaps a Cyltrol valve?

I reckon the noise is kettling caused by the acumulation of scale, rust and sludge in the boiler. It must be thinking about pegging out by now.

You could give the syst a flush and refill with fresh to remove old soft sludge, but the old scale is probably firmly fixed to the exchanger and won't wash out.

Sentinel do a Boiler Noise Reducing fluid which you can mix with their inhibitor, slow acting (weeks) but seems to help a bit. You will have to use a brand compatible with the chemical you've already got.

I take it you have the boiler running night and day, with the young child and cold weather. If you were able to turn it off at night then the nocturnal disturbance would stop. Has it got a timer?
 
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the system as i can see it is a baxi bermuda 520 back boiler - seperate 3 speed circulation pump (possibly in addition to boiler circulation pump), fed by header tank in loft. H/W fed up to cyclinder in airing cupboard so assume it is pumped not gravity. No idea about bypass valves etc, but all works absolutely fine.

It appears that whatever is switching the pump on and off is operating ok at fire up, but then switching the pump of early. Perhaps there is some sort of thermal switch on the boiler which controls the pump that could be at fault by reading boiler temerature incorrectly?

If i power the pump manually (fit plug and switch it manually) the problem does not occur as i keep the pump circulating for a minute or two until the residual boiler heat has gone (which i would have expected to be normal operation). So it seem that the problem is switching.... however i do not really know what is controlling the pump on/off.

I did flush the system before adding the descaler/cleaner, and the oxide was minimal on draining. The cleaner has been in the system for one week out of the recommended 4 weeks.
 
I would expect the CH circulating pump to be controlled by a room thermostat, isn't that right?

If you control the pump manually, and keep it off, does the hot water cylinder get hot?
 
i am not sure. there is a switchmaster 400 timer (h/w&c/h - h/w - constant & timed) and wall mounted thermostat in the hallway. All looks to be original equipment.

I did think that all the timeswitch did was to switch power on/off to the boiler when the roomstat called for heat, and that the boiler itself controlled power switching to the pump.

My knowledge of back boiler systems was non existent until i moved in, and i haven't tried to keep the pump off and check for h/w. I can say though that the radiator 'behind' the h/w cylinder is always hot whether heating/hw on or off.
 
The boiler does not control the pump. The lead that powers the boiler also feeds the pump.

Is the pump really switching Off? Have you metered the L&N to see if power is being disconnected? Have you done the same at the boiler to see if the power is going off at the boiler? Assume nothing.
 
i haven't metered anything as yet, just listened to the pump which can clearly be heard switching, and the vibration of the pump can be felt when it is running. likewise the vibration stops when the pump switches off.
If it is the timer that switches the pump, then perhaps it is time to upgrade this unit to a more flexible electronic control?
 
No, I think you'll find that in your current installation, the timer controls everything, then, subject to timer being on, the wall thermostat turns the pump on and off, and (probably) the boiler thermostat then turns the flames on and off.

If you have a thermostat on the hot water cylinder, then, additionally, the flames will only come on if either the wall stat, or the cylinder stat, or both, are calling for heat as well as the boiler stat.

I think Gaz had in mind an additional "delay" timer to keep the pump running after the wall stat said off (that right, Gaz?)
 
The mud is becoming a little clearer. thanks for the responses.

I am interested in the kit you mentioned, but i am still a little confused as to why the boiler would run as it does, with the pump shutting down before the burner, and what is switching it off. It would seem from the previous replies that the timer enables power and the stat switches it on/off. surely tho', it should switch both the boiler and pump off at the same time, as it switches them both on.

If this is how it should operate, why is the pump switching off before the boiler?

It makes complete sense to me that the pump should run on a little after the boiler, which the kit would address.
 
Almost certain you will have a bog standard gravity HW and pumped CH installation.

In such a setup, HW part of the timer fires the boiler. When you ask for CH, the pump runs (via a roomstat usually). But the pump running on its own will not heat the rads. An internal link in the timer activates HW channel which in turn fires the boiler.

Instead of overloading the brain cells, why not check your system and post what you have. You are assuming too much. Metter or even a neon tester will tell you loads.
 
Your boiler has a cast iron heat exchanger and is designed to work without any noise even if the pump is not running as it would do in a gravity HW configuration. So if you are getting loud banging and popping sounds going through pipework you have one of 2 problems the boiler stat is out of calibration and is allowing the water to get far too hot and needs changing or the gas valve has had it and is staying on (when it should be off) or is passing slightly allowing the water to get far too hot also. New valve req
 
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