Hi, just moved in to my new house. It has an old back boiler in it (Baxi Bermuda 551), gravity hot water, a Honeywell ST559B control, and a central heating thermostat. Just some general questions so I can get to know the set-up better:

1) The cylinder doesn’t appear to have a thermostat. I assume this is correct with a gravity fed sytem? If so, when the central heating is on for a long time, the hot water becomes almost scalding hot, and vents to the tank in the loft. Is this is normal, and just the cons of having an old set-up?

2) When the heating thermostat cuts out at the desired temperature, does that stop the DHW heating up as well (when the controls are on the heating + water function)? So could you have the heating on all day at a low temperature and this mean the DWH is not constantly on?

3) The radiators all seem to get warm, but you can really hear (what sounds like) the water rushing through them the whole time the boiler is firing. No banging or anything, just noisy operation? Would bleeding any air out help?

4) The back boiler really makes some lovely noises, half of which I think might be wind coming down the chimney. Sometimes sounds like a kettle. Are back boilers of this age just noisy in general?

5) If I attempt to bleed the radiators, am I right in thinking that the system tops itself up, unlike a combi set-up?

By the way, it’s all going in the summer hopefully, so it’s not the end of the world. If I can just make it quieter I’ll be happy.

Many thanks in advance.

Anyone?

The kettling noise from the backboiler is due to it's age from years of sludge build up in the system. It probably good do with a good power flush, but if your changing it in the summer then I would suggest live with it for now, or add some central heating cleaner or noise reducing chemicals. Sentinal are good.
The temperature on your cylinder is determined by the temperature setting on your boiler. Suggest you lower this to minimum and only raise it if the central heating side doesn't heat up due to really cold weather.
The system is feed by a Feed & expansion tank in your loft. So if you bleed a radiator it should automatically top the system back up. If it doesn't your system feed may be blocked.

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Your problem is now our problem

if you're going to rip it all out, then this is of no use, but,
Honeywell C plan would control the boiler in your scenario but its time and expense when all you really need to do (as above) is turn the boiler stat down, limits the temperature the boiler will fire to.

If its the same as mine, the run to the HW cylinder is in 28mm with a 28mm coil in the cylinder, this is because the thermo-syphon needed works better with the larger the diameter pipe.

Thanks for the replies.

I'll have a look at Sentinal and the like, thanks. I assume nothing really bad "should" happen as a result of adding it in? I suppose it could dislodge something. Where does all the crap go from the system when you add the cleaner, etc?

How do you get to the temp setting on the boiler? If it means removing the front fire, I'm not allowed to do this, am I? Or is it accessable another way, etc?

Many thanks again.

it's just a metal flap/panel under the fire itself, should be hinged to swing downwards

behind that should be the "temp" dial (just min, 1 -3, max),
orange igniter button and grey gas "cut off" valve if its the same as my barracuda 57/4M (manual ignition)

or if its the electronic ignition then you wont have the igniter button.

just pulled the front off to see the boiler control and it's on the highest setting. the house doesn't get hot as it is though so am loathe to turn it down - the missus will cry.

i am tempted by the sentinel x200 though. i guess i just tie up the ball valve, drain the system down a little and add it to the f&e tank?

thanks guys.

Nope

The way it works is the temperature of the gravity circuit is controlled by the boilers thermostat. All the time the hot water is on there is power at the boiler and it just cycles on the stat which is why it fires up for a few mins, turns off for a few mins etc.

You have probs noticed you can't have heating on it's own you have to have hot water.

When the heating/hot water is on the boiler still cycles on it's thermostat but the room thermostat is used to turn the pump on and off which gives you the heating

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When the cleaner has done it's work flush the system and refill it and add an inhibitor. The crap will be flushed out.

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Thanks for the replies.

Razor, am I reading your comment correctly (god, I hope I am!)? Are you saying that the boiler temp knob only relates to the DHW side of things? It was on "High" (out of off/low/1/2/3/4/high) so hopefully that would explain why the water was so hot and why the central heating wasn't too effective.

If I turned this knob down to 1 or 2, would the central heating be negatively affected by this, or is it completely under the control of the pump? WOuld it take longer to heat up, or in theory be quicker because I'm not draining so much energy on the DHW side of things? If i turned it to "off", what would happen?

The place has an electric shower, so I don't need the DHW hardly at all!

I'm waiting with baited breath here! No doubt I've read this wrong...!

For heating set it at 3 and try it, you can always tweak it up a number if it gets cold.

The numbers are guides, every property will be slightly different.

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yep, confused again - does the temp control affect the heating temp or just the DHW temp?



ta.

Both

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As a wood butcher I try not to stick my nose into too many plumbing questions but as a past user of a Baxi back boiler I can say that in my understanding the temperature control on your Baxi boiler merely governs by how much the boiler will heat the water passing through it, it's not a set temperature it just raises the incoming water by a certain amount, the temperature the water exiting the boiler will reach depends on the temperature it comes in at.

I used to put mine on low in summer and high in winter, (also had a roomstat for the heating side of things).

HTH

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knob on boiler controls temp of all the water running through it,
mine's set on 3 at the min, waters plenty hot enough and heatings on. :)