Turn your preheat option off on your combi boiler!

SYNERGY

Mr_Ted wrote: »

That is typical of someone who has to do research and has no experience

"SOME" is the keyword

Much as not all Combi's are instantanious and the older type have cast iron or steel heat exchangers and thermal shock can be an issue.

Try jumping into a freezing lake and see what happens to your body, dont bother to report back tho ?

I repeat to all posters as I have said on here ARMCHAIR ENGINEERING is dangerous, a diagnosis can only be carried out with FACTS of the issue by a QUALIFIED ENGINEER!

That is typical of someone who has to do research and has no experience

Sad that you are trying to insult me Ted, a bit of my background.

I started my apprenticeship in 1962 at 15 years old, when it was a six year apprenticeship.

Worked for 43 years and retired at age 58, my choice, I worked every hour going to be able to retire early and be happy and comfortable for the rest of my days.

I can still wipe a joint, form a lead box, lead valley, etc. still have a bit of the old red rubber gas pipe most appliances used, mole skin, lead shavers and so on.

In those days all the old tools required to perform most plumbing or gas jobs could be carried in a bag on a push bike.

As times moved on so did I, I bought and used all the latest equipment ( gas, combustion gases, temp probes, electrical and so on) to service and repair what were then the upcoming boilers and systems we have today.

.........research and has no experience..........

In the old days, experience was all that was required.Today, in many industries, technology moves so quickly that both go hand in hand.

My experience and research allowed me to make a very good living, either on their own wouldn't have.
.......and the older type have cast iron or steel heat exchangers and thermal shock can be an issue.

Can you answer me a simple question ?

In 43 years, the only damage I ever came across and those could be counted on one hand, caused by thermal shock was with, in the main, the old cast iron back boilers where they had been run dry, were still hot, then cold water introduced into them and of those 50% were coal heated back boilers !

So my question, how many boiler heat exchangers , domestic, have you come across damaged by thermal shock and how did you prove that thermal shock was the reason they failed ?

Cardew

Mr_Ted wrote: »

That is typical of someone who has to do research and has no experience

"SOME" is the keyword

Much as not all Combi's are instantanious and the older type have cast iron or steel heat exchangers and thermal shock can be an issue.

Try jumping into a freezing lake and see what happens to your body, dont bother to report back tho ?

I repeat to all posters as I have said on here ARMCHAIR ENGINEERING is dangerous, a diagnosis can only be carried out with FACTS of the issue by a QUALIFIED ENGINEER!

In the few short days you have graced this forum with your presence, you have done little but tell us how brilliant you are and insulted anyone who has disagreed with your opinions and advice.

I am no gas fitter, albeit I am an Electrical Engineer(Chartered) as are several others on this forum. It is actually fairly easy to pick out those plumbers/gas fitters who are both knowledgeable and helpful - e.g. SYNERGY, Canucklehead, aelitaman, gas4you and even bengasman(despite his acerbic posts) and others.

Your posts have largely been neither helpful or accurate and some advice you have given has been plainly incorrect.

If you don't want to become a figure of fun - ridicule even - you need to change your attitude, or get a new identity.

Mr_Ted

Synergy I find it sad that being new here that so many make assumtions and ridicule and dont expect a terse response to what I may have said and it is or maybe is not experience based or factual or has been experienced?

From the very outset, and I see it on the posts of others, there is an arrogance in the responses that are far from helpful to the poster, and it should aso be noted could be dangerous to apply without the correct knowledge and qualifications!

Now for my background, and I also spent my youth on a push bike with 2 bags of tools on it, but it would add that these were tools that allowed me to do plumbing work and all and every type of gas work!

I also started my apprenticeship in 1962 but mine was as a gas fitter for a gas board, 5 years, city and guild intermediate & finals gained!
Pre conversion and conversion, so on towns and natural gas
I moved on to gain a wider experience and was qualified in Commercial & Industrial gas
Wet and Warm air systems and all appliances
Oil and gas blown package burners and Combustion
Domestic and Commercial Controls
LSP plant and water Hygiene, and Cooling towers
Pressurised systems and pressure sets
Advanced Plumbing
HVAC and all that that encompasses
Approved and Authorised person for LTHW and MTHW systems
Supervision and contract and Work Services management
and I kept up to date with modern systems and appliances

I was responsible for QA, profitability, employed labour forces, contracted maintenance services, tendering and letting contract and hiring and firing!

Not only that but what I found, which is sad, was that far to many engineers with gas qualifications did not have the experience to do the job properly, but I nurtured those that were prepeared to be responsible and knowledgeable.
I have come across situation whereby Certification was 80% deficient, unprofitable or false, and turn that around to be 100% correct and profitable.

Those that just wanted to blast a vacuum cleaner around the boiler casing and spend hours in the cafe and also skive of at 1PM, and not be responsible were replaced by those that were responsible and for that they had flexibility and understanding!
Most of those guys turned to me for guidance if they had a problem and received it, as they had not had my experience, and they the customer benefitted from not having down time on their services, unless it was absolutely essential as parts could not be source or already stock items!

I have on many occasion had to physically show engineers how they need to strip an appliance or explain how a system works.

I had and have an ethos that you can learn something everyday, but by experience not hearsay!

To elaborate a bit further I can and was qualified to install, maintain pretty much everything from a domestic property to an office block, and have at some stage in my life done it!

From your stated experiences synergy you were a plumber, not a gas fitter or certainly wernt in my area as only gas fitters were qualified originally to work on gas although many plumber did do it as legslation had not been introduced at that time.
I would also state as fact that it was the gasboards gasfitter who had to resolve botched jobs by plumbing companies, and finish contracts that plumbing contractor couldnt, usually because the board itself had let the contract to the plumbing company in the 1st place.
It was also a gasfitter who went out and completed repairs that service engineers couldnt when the board decided to introduce them and give them 6 weeks training before letting them loose on the public?

In my 48 years I have come acroos combi boilers that have had split heat exchangers, and hot water storage jackets, and would ask you if what i say may not be correct why do modern boilers have a bypass???
I think you should consider that there are certain built in system that are their as preventative measure as well as practical?
Preventative systems are inbuilt in some instances to prevent thermal shock from having an adverse effect on heat exchangers by way of deterioration and degradation of the metals of construction which is not usually instantanious but gradual if not catered for!

You must have in your apprentiship learned the effects of annealing and hardening of metals and how those processes were achieved and the effects on the metal structure and stability?

Ultimately if it says how an appliance should be set up and used in a manufacturers manual then that is the law as to what should be done and overrides all other legislation, or opinion!

Anything I have said is what I have experienced but there is one caveat that should be considered on a forum like this, how a systems controls are set by a user for whatever reason is down to that users preferences, others have differing opinions or experience, when it comes to fault finding or working on an appliance that is a different matter and only a QUALIFIED person should carryout any repair.
All responders should consider that they may be encouraging UNQUALIFIED people to do something that is a danger to them, and others!
It should also be considered that gas appliances and gas installations can only legitimately be worked on by Qualified gas engineers(about whom I have reservations) as also applies to pressurised system!

So buyer beware, and responders also beware of their responsibilities!

Sorry Cardew but you have said it yourself, how are you qualified to refute the accuracy or correctness, opinion may differ which is a different matter, about what I may have said.

I can live with myself also but I will also defend myself and you should really think about who casts a 1st stone???
Advise on here should be considered by the written word of the original poster, not reality of the factual circumstance, guessing is dangerous!
Being a long term member on here is not qualification to answer all matters!

Possetjohn

Advise on here should be considered by the written word of the original poster, not reality of the factual circumstance, guessing is dangerous!

Mr Ted, I have to say you are the one who has gone far off the original post!

I bet millions of people already know this but I just had my boiler serviced and the guy from British Gas told me to switch the "preheat" option off for the water. He says it is wasting massive amounts of gas by keeping the water hot all the time, ready for use. The alternative is to wait a few seconds for the water to heat up as and when you turn the hot tap on.

You were the one that has introduced the discussion about damage to heat exchangers by thermal shock with very little in the way of evidence and have refused to give any specific examples.

The reason for preheat is to prevent thermal shock which could damage the heat exchanger!!!!!!!!

As has been said before the preheat function is purely to give a quicker feed of hot water to the taps on demand or in some cases a temporary higher flow rate. If it is a safety feature why does the boiler manufacturer allow it to be switched off by the user?

The small brazed or welded plate heat exchangers are quite capable of standing the thermal shock of the temperature differences involved! The maximum possible temperature difference in a modern boiler would be when the boiler was running central heating at a high temperature and the incoming mains water is a its lowest winter temp when a hot water tap is opened. Maximum of 80°C. Similar but larger heat exchangers to these are used in the chemical industry to generate hot water from steam and cold water with excellent reliability!

In my 48 years I have come acroos combi boilers that have had split heat exchangers, and hot water storage jackets, and would ask you if what i say may not be correct why do modern boilers have a bypass???

Correct me if I am wrong (and I'm sure you will) I thought the bypass was was to protect the pump and primary heat exchanger in the event of no or severely restricted circulation. This can happen in a system with all thermostatic valved radiators with all the valves turned down. I find it difficult to see how it would happen on the heating side of the DHW plate heat exchanger except by a strange failure of the diverter valve. In the event of sludge in the primary circulation then the primary heat exchange and the bypass itself will be all affected!

Going back to the original post, the heat losses in the gas fired pre heat option are most influenced by the heat losses in the primary and DHW heat exchangers and linking pipes during the cool down periods between the intermittent boiler firing rather then the heat loss from the small storage tank!!

Cardew

Possetjohn wrote: »

Correct me if I am wrong (and I'm sure you will) I thought the bypass was was to protect the pump and primary heat exchanger in the event of no or severely restricted circulation. This can happen in a system with all thermostatic valved radiators with all the valves turned down. I find it difficult to see how it would happen on the heating side of the DHW plate heat exchanger except by a strange failure of the diverter valve. In the event of sludge in the primary circulation then the primary heat exchange and the bypass itself will be all affected!

My understanding also - this from the Myson website:

Automatic Bypass Valve

What is an automatic by-pass valve?
An automatic by-pass valve is designed for use in domestic central heating systems. Its purpose is to maintain constant pump pressure within the system.

Back to top

What are the advantages of an automatic by-pass valve?
An automatic by-pass valve ensures minimum water flow rates through the boiler. It reduces system noise associated with high pressure pumps. It eliminates the need to fit an uncontrolled radiator to act as a system by-pass and it also increases system efficiency. The automatic by-pass valve also aids the operation of thermostatic radiator valves.

Mr_Ted

Cardew wrote: »

My understanding also - this from the Myson website:
Automatic Bypass Valve
What is an automatic by-pass valve?
An automatic by-pass valve is designed for use in domestic central heating systems. Its purpose is to maintain constant pump pressure within the system.
What are the advantages of an automatic by-pass valve?
An automatic by-pass valve ensures minimum water flow rates through the boiler. It reduces system noise associated with high pressure pumps. It eliminates the need to fit an uncontrolled radiator to act as a system by-pass and it also increases system efficiency. The automatic by-pass valve also aids the operation of thermostatic radiator valves.

That is correct although there are some inaccuracies in that statement:-

"maintain constant pump pressure within the system." the pressure within a system is not maintained by the pump, the use of a bypass valve, as described in this statement is to prevent a loss of flow through the heat exchanger were a situation to arise that all radiator were to be shut down due to TRV which would cause the "pump" to cavitate and the heat exchanger to rapidly heat to a point that the boiler stat would shut the boiler down but it may be possible that without flow through the heat exchanger a latent heat build up could occur resulting in other problems!

"pump" is the wrong term for a heating circulator, circulator is the correct term as little pressure is produced. There may be a positive pressure on the outlet of the circulator, but a negative pressure at the inlet, however this is equallised thoughout a system very quickly and "flow" is achieved by the differential between the inlet and the outlet of the circulator due to the rotation of the impellor!, By varying the impellor speed the pressure is not increased in the system the flow is!

"An automatic by-pass valve ensures minimum water flow rates through the boiler." which is to distribute the heat throughout the system and will also prevent thermal shock within the heat exchanger, be it from and immediate ingress of cold water, or a latent heat build up due to no flow!

"increases system efficiency" as the flow through the heat exchanger not only prevents thermal shock it pre heats a percentage of the water flowing through the heat exchanger!

"It reduces system noise associated with high pressure pumps." firstly it should be high volume flow circulator, and the noise prevention would be that associated with rapid expansion of the heat exchanger due to heating and cooling(thermal shock) which can cause the boiler to make crackling type noises, or the noises caused by cavitation were the circulator to be running and unable to produce a flow due to all TRV's being shut!

"The automatic by-pass valve also aids the operation of thermostatic radiator valves." only by maintaining an equal flow through the valve as the operation is via temperature control of the TRV head on a valve within the valve body which controls the flow!

( of post, but if you were to put a hose on the inlet of a heating circulator in water and run it, it would be unlikely to draw water on its own, a pump would!)

spinningsheep

good god mr ted you are at it again!what is wrong with you you nasty little man! as cardew has said in the short while you have been posting on these forums you have done nothing but antagonise and insult people, why?! We cant all be wrong, take some Christmas spirit and stop being so vile!!!

C_Mababejive

Pre-heat...?Bwwahhaha...dont have one,but i do have a nice tank of hot water in the cupboard..

Dave_save

renegade wrote: »

I have a Worcester and mine does not have that facility, when the heating is on the water is on, can't have heating and no hot water... can you?

I can control DHW preheat via the timer on the model I have. This is completely separate from the central heating. It may be that with your particular model it just needs the correct timer, but I know some of the Worcester combi boilers aren't able to 'time off' the preheater.

C_Mababejive

macman wrote: »

It's not a combi then. With a combi, the CH cuts out when there is a demand for hot water.

What a step back ...my boiler can do both at the same time and has a heat input of about a quarter of a combi

I do think it unfortunate and unproductive when discussions turn into d!ick comparing competitions..