Worcester Boilers - Slight Confusion

[TheScullster]

Hi Guys

A number of posters have given good reports of Worcester-Bosch boilers so I am considering one for my heating upgrade.

Can someone who knows help me with some clarification please?

On the web site, the 29HE is stated as suitable for a small to medium house, whereas the 28HE states medium to large. How can this be when the 29HE has the slightly higher output?

The larger models state that a modulating pump is included in the "system" boiler options. Is this the same as a Grundfos Alpha type model, and would these be compatible with the 29HE?

I have heard that some system boilers have an inaccessible expansion vessel which means major dismantling in the event of problems with diaphragm etc. Is this the case with the 28HE?

To be honest, I am undecided whether to go:

a) 29HE with external pump and leave system as is (with expansion tank in loft) b) 29HE with external pump but convert to sealed system by fitting expansion vessel in airing cupboard c) 28HE and convert to sealed system

My house is 1970s construction with mostly new rads that I have replaced myself.

Any thoughts/clarification appreciated

Phil

[Doctor Evil]

They are about the same. The marketing people got it wrong.

The pump is modulated by the boiler controls, not an Alpha which has its own controls.

No. it is on the side and slots out. Some other makes have them at the back of the heat exchanger between the wall and the exchanger. These are difficult to replace. Most tend to cap the old vessel off and fit an external vessel on the heating return.

Go to the B-W web site and download the service manual for the boilers. It clearly shows the vessel location.

This is the easiest. Just a straight exchange.

This is best as all is in one box.

With these models the electrical power must go through the boiler first. Yo u may have a bit of requiring of your controls.

[RedOnRed]

From what I can tell the 29HE is a standard boiler while the 28HE is a system boiler, which you've kind of answered below anyway.

[Christian McArdle]

Do this. Gravity fed systems are a real PITA. Sealed is the eay to go.

Christian.

[Dave Plowman (News)]

Explain? There seem to be a lot of problems mentioned here with them. Of course if you don't have room for a header tank, fine.

[Christian McArdle]

They're nothing compared to problems with tanked systems.

Some problems with gravity fed, I'm sure there are more.

1. Hard to refill. Air locks abound.
2. Unlimited loss of water in the event of a leak.
3. Failure to detect leaks for long periods due to replenishment.
4. Pumping over, introduces new water and air, leading to corrosion.
5. "Debugging" circulation issues very difficult and can prevent high pump speeds.
6. Incompatible with most modern boilers.
7. Requires pipework in loft, which may freeze and leak.
8. Venting arrangements may be unreliable due to long or convoluted vent pipework runs.

Christian.

[Dave Plowman (News)]

I've not had any problems in many years with mine. Apart from air locking on filling, but that's easily got round.

I'd agree that one, but how often do you do this?

Put a stopcock in the cold water feed if it bothers you. Then you're limited to the contents of the tank.

But when a pressurised systems loses pressure, most just seem to top them up, so the same thing?

Badly designed in the first place, then.

I'd rather not move the water around too fast due to noise.

Why is that?

The same applies to a storage water system, and I'm certainly not giving that up.

Again, down to design and installation.

Thanks for the info, though. But it still seems to me just more thing to go wrong, for no obvious benefits other than ease of installation.

[Christian McArdle]

This is only safe if the boiler has a manual reset overheat lockout (i.e. is suited to sealed pressurised operation). The safety "mechanism", if you can call it that, for a boiler without an overheat lockout is to have an uninterrupted vent to get rid of the steam, and an uninterrupted independent path for quenching water, so it can boil away merrily until someone bothers to turn it off. With a stopcock on the feed, it will run out of water and possibly burn the house down.

Well, the clues are there, you can choose to ignore them.

But can be difficult or impossible to achieve, with the tank in the loft and the boiler in a kitchen, in the rear "extension" bit.

Christian.

[Dave Plowman (News)]

It was common practice years ago to have no feed at all to the header tank. Servowarm, for one. And of course the first sign of the level being low is the upper floor rads not working.

Boilers in those days didn't have overheat lockouts - but I can't remember it being common for them to start fires. ;-)

[Doctor Evil]

Absolute madness.

[Doctor Evil]

There are one pipe feed/expansion systems using a header tank. In this case the boiler must have extra protection, such as dry fire protection. They are pig to get the air out if no adequate auto air vents are installed.

[Dave Plowman (News)]

Stick to things you know even less about.

[Ed Sirett]

How long is a piece of string. small/medium/big house ?

Unless your house is really large I suspect that all these models are bigger than you really need.

Read the SealedCH FAQ for back ground reading.

The system boiler contains the pump and this is good because the boiler control the pump speed to match the gas rate.

I'd definately go for c but check if you really need the boiler to be that size.

[Doctor Evil]

You are just plain dangerous.

[Tony Bryer]

An ex-plumber I worked with reckoned that this was because Servowarm installers were not to be trusted to cut into an existing main - they could do new copper and compression joints but not necessarily anything else.

[Dave Plowman (News)]

Heh heh. My theory was it simply to save money.

[mungoh]

Or it could be to encourage plumbers to top up the tank by "internal" means so that they could get their 15 minutes of fame via a "dodgy builder" television programme? Mungo

P.S. Now a proud owner of a 40Kw Worcester Bosch condensing boiler. I know it's the summer but on the cold mornings when the boiler kicks in it is amazing how fast our radiators warm up now compared to the old 24Kw boiler.

[TheScullster]

Thanks Ed

This thread has lost its way somewhat, so I will start new thread with subject Help with Boiler Selection

Phil

[Ed Sirett]

I'd go along with the save money idea. After all they would have to do the gas connection so they'd have to up for that.... um..... Yeah Right.

They used to justify the 'feature' by saying how that any flood would be limited, a somewhat negative approach IMHO.

They also set fire to my neighbours house (ceiling void and blow lamps) when they had there CH installed c. 1980.

[Dave Plowman (News)]

Yup. If that was the only reason, you could fit a stopcock before the ballvalve in the cold water feed and leave it closed until needed - to save carrying buckets of water into the loft.

Oh dear. They were the sort of Kwik-Fit of central heating, but like them probably criticised more than they deserved. Wonder what happened to them?