Flow and return the wrong way around????

delboyd · 6 Jan 2007

Cheers for all the info,

Namsag, I'm over in East Northants so if you could recommend somebody in that area that could take a look at it for me I would be grateful.

lor · 6 Jan 2007

East Northhants is that the same as North East hants ?

delboyd · 6 Jan 2007

The People's Front of Judea?

Agile · 6 Jan 2007

croydoncorgi said:
Yes - maybe OK on SOME boilers, eg. those with a stat in a pocket in the heat exchanger body.
But it B well isn't on Suprimas because the sensors (both main thermister and overheat stat) are on what's SUPPOSED to be the Flow pipe. If it isn't - well, you work it out!!!

Even a Suprima will still work adequately when the flow is reversed.

The thermostat is then subjected to the return temperature which traditionally is only 11°C below the flow.

The only effect a householder would typically notice is that the boiler output is 11°C above the set point on the boiler thermostat.

This kind of problem is normally only found by a heating engineer when investigating something else.

Tony

croydoncorgi · 7 Jan 2007

Tony - this is the FIRST OCCASION when I can respond 'Utter and complete rubbish' to one of your responses. You seem to be suffering from 'finalitis' - an irresistible urge to have the last word!

If I hadn't actually EXPERIENCED a MAJOR problem due to this fault (actually very recently), I'd either have said as much or not commented at all.

In MY case, what ACTUALLY HAPPENED was that when the boiler started from cold it soon BOILED, causing overflow of the F&E, steam in the loft, noises from the boiler, boiling water falling outside the back door, etc. (as YOU might expect, if you'd thought about it!) LONG BEFORE the heat got round the radiator pipework and back to the boiler to affect the temperature sensor.

Once I'd worked out what was wrong, I found that the boiler would only work comfortably with the temperature adjustment turned to absolute minimum setting. (It was not possible to tackle pipework changes immediately.)

Once corrected, all has been peace and silence (and well-controlled heating) ever since.

Agile · 7 Jan 2007

If the Suprima is correctly sized to the installation and has adequate flow then it will operate reasonably well when the flow is reversed.

This model is one of the worst for incorrect installation design!

All 120s should have 28 mm pipe and a larger pump but virtually none do.

It seems to have been the norm to over specify the output power by factors of typically two times.

I appreciate that you just like to disagee but could you explain just how that one could boil if it had the correct water flow rate? It would have only 11°C temperature difference if properly matched.

Tony

croydoncorgi · 7 Jan 2007

The boiler is a Suprima 80, as you suggest driving 22mm pipe.

As you are also perfectly well aware, the 11C degree differential between Flow and Return is more hope than expectation for the great majority of installed systems DURING WARMUP, ESPECIALLY if they have control PCBs of the level of complexity of the Suprima AND burners with little or no modulation capability.

What ACTUALLY happens, especially if the CH part of the system is running by itself, is that the Flow temperature reaches its setpoint, so that the boiler cycles off and back on, SEVERAL TIMES during the warmup period, before the whole system reaches a stable temperature with whatever differential it can achieve. In many cases, especially when hot water is being heated too, the differential becomes MUCH LESS than 11 degrees.

With the broken system referred to, the ONLY way to achieve your 'stable state' scenario was to inch the system up to temperature by manually turning the boiler off each time it stressed-out, then leave the CH running (with a 9C degree Flow / Return margin!) 24/7. Clearly unacceptable.

If you're suggesting that the typical installer actually bothers (or indeed is able!) to calculate heat losses and flow rates to the level where the resulting system will MAINTAIN a given temperature differential from cold through warmup to stable operation at the boiler Flow setpoint, that's also a completely unrealistic fiction. It hardly ever happens. And it's also a waste of time, IMHO, given the extra features of boiler controllers and burners now available.

lor · 7 Jan 2007

agile, hi,
Suprima 120 needs a 25/55 light commercial pump.
Potterton state the pipework should be 35mm to within 300mm of the boiler.

Corgiman ,hi, i've been off work for 3 months following op.

Agile · 7 Jan 2007

croydoncorgi said:
The boiler is a Suprima 80, as you suggest driving 22mm pipe.

If you're suggesting that the typical installer actually bothers (or indeed is able!) to calculate heat losses and flow rates

Your Suprima 80 gives 24 kW whereas the average 3 bed semi needs about 10-11 kW so it was over twice the power required and the 22 mm tube rather inadequate into the bargain. Not surprising it would boil!

The Suprima does not modulate and should not be range rated according to the sticker on it although I dont see any reason not to compared with similar boilers.

I agree that installers dont bother to calculate anything. Not heat losses nor gas pipe sizing. With their energy efficiency cert they are meant to know how though!

I still say that a correctly rated and piped Suprima will still operate adequately if its reversed.

Virtually all the installations I have ever seen are totally over powered. One in a semi uses a Suprima 120 with 7 m of 22 mm tube back to the motor valves. It heats up for one minute then goes off for four minutes! It seems totally wrong to me but I could not think of a reason not to issue a CP12 for it.

Tony

Click to expand...

kevplumb · 7 Jan 2007

FWIW

i once fitted a pump the wrong way (friday at 6) and the flaming thing would not heat up

kept short cycling

croydoncorgi · 7 Jan 2007

And, apart from not coping with your finalitis, your point is??

Are you SERIOUSLY suggesting that it would be WORTHWHILE (ever!)to take out a boiler because some prat oversized it? Why - apart from marginal efficiency loss? What is the problem with correcting the plumbing and letting it die a natural death. Given it's a Suprima, that will probably be sooner rather than later - although I'm bound to say that all the ones I've fitted with new-type PCBs seem to be lasting 'way too long!

And what about all those 28 and 29Kw combis. Yes - they CAN modulate down to 8Kw or something. But with a cold CH system, they tend to push out much more than your idea of the actual heat requirement for the situation - and the house warms up quicker! No big problem there either.

Agile · 7 Jan 2007

croydoncorgi said:
And what about all those 28 and 29Kw combis. Yes - they CAN modulate down to 8Kw or something. But with a cold CH system, they tend to push out much more than your idea of the actual heat requirement for the situation - and the house warms up quicker! No big problem there either.

I always range rate the CH output from a combi.

Many of the later models come on with a reduced power anyway for about four minutes and see what the return does. If it warms up then they stay on at a low level if not they ramp up towards the maximum CH power set by the installer ( if he has bothered which is rare ).

Tony

festive · 31 Jan 2019

croydoncorgi said:
Be careful to re-confirm the diagnosis.

- the pump may be the RIGHT way round but connected to the wrong pipe coming from the boiler. Ways to confirm this: the boiler will be VERY unhappy, overheating frequently and locking out. When it starts from cold, the RIGHT HAND of the two pipes coming out of the top, left of the boiler will get hot first. This SHOULD be the Return pipe and get warm some time LATER than the lefthand (Flow) pipe. The reason the boiler is unhappy is that the temperature sensors are attached to the lefthand pipe and only see any heat LONG after the boiler has cooked up!!! The easiest way to correct this is usually to swap the pipes over near the boiler.

festive · 31 Jan 2019

I know this is an old thread but exactly the symptoms I have on a WB 18/25 Greenstar and confirmed by an engineer.

Would this also cause an issue with efficiency of the boiler?

45yearsagasman · 31 Jan 2019

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Flow and return the wrong way around????

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