identifying an existing CH system design?

[JB]

Are there any links to diagrams etc which would help me identify the CH system I have installed in my late '70s house. It's a pretty basic system with gas-fired boiler in the garage, feeding an indirect cylinder in the airing cupboard above with a circulating pump on the boiler return pipe next to the boiler. There is no cylinder thermostat or room stat anywhere in the house. The controller is a single channel electromechanical timer. There is a manual valve to 'switch' between hot water and radiators. I'm looking to replace the cylinder soon with a new one and retrofit a modern electronic programmer with a cylinder stat and room stat. The bit which confuses me is where do I put the 3-way valve (or do I use a 2-way valve in place of the manual valve)? Any help or links would be much appreciated. Thanks,

JB

[IMM]

Sounds like a real cheapo system.

As this is about 30 years old I would seriously consider replacing the boiler. A modern boiler will save you a small fortune in gas, How many bathrooms? showers? etc? Do you need fast bath fills etc?

The easiest way is to fit a high flow combi if the mains are suitable; Alpha CB50, Worcetser Bosch 40 kW condensing combi, etc. Cold water in hot water out. Remove the 3-way valve and cylinder and tank, giving losts of space, and very easy to connect up. Flush the pipes first. Then fit a Honeywell CM67 stat/programmer which is two wires back to the boiler. The simplest and most cost effective way to go and all the ills are recified giving high pressure mains showers.

[Set Square]

From what you say, your system is fully pumped but with the water going either to the HW coil or to the radiators, but not both at the same time. What does this manual valve look like - does it have one input and two outputs - maybe arranged like a tee-piece? If so, you could fairly easily convert your system into a Y-Plan by replacing this valve with a 3-port mid-position valve. This would support room and cylinder stats - which would provide a "boiler interlock", so that the boiler would only run when either or both circuits required heat - and would also enable both circuits to be on at the same time when required.

There are schematics and wiring diagrams for several different "plans" at

your pipework doesn't lend itself to using a Y-Plan, you could instead go for an S-Plan (which many people believe to be technically superior anyway). This uses two 2-port zone valves (one in each circuit) each driven by the programmer and respective thermostat. Each valve has a set of contacts which are wired to turn the boiler and pump on when the valve is open - i.e. when there is a demand for heat from either or both stats.

With either system, if you use a conventional 2-channel programmer for overall control plus a programmable room stat, you can have completely independent control over when the HW and CH come on.

[IMM]

Best no silly plan and use two plumps with check valves and a relay in a box on the wall.

Best still fit a high flow combi as the boiler will be near the end of its life. So much easier and effective in speed of installation, ease and cost..and power showers for free.

[JB]

I'll have to give this idea a closer look. Thanks very much for both of your advice. cheers, JB

[Set Square]

Whilst you could undoubtedly save a lot of fuel - and money - by installing a more modern boiler, you can also make a lot of improvements to your current system, and benefit from some of the savings, for a fraction of the cost - without replacing the boiler at this stage. Installing zone valves and thermostats so that the boiler and pump only run when needed will make a tremendous difference - especially if you also put TRVs on most of the radiators.

If you are replacing the cylinder, buy one with fast recovery (big heat exchanger inside) and well lagged with integral foam.

Be aware that - according to our friend IMM - combi boilers are the answer to every maiden's prayer. In reality, they are not - and there is a lot to be said for keeping a stored hot water facility.

[JB]

I'll have to admit that is what I was originally going to do. Replace and move the cylinder, fit TRVs throughout, and keep the old boiler until it gives out. I've only just replaced the pump (not bad for 25yrs old) but the boiler is in excellent condition according to the BG engineer who serviced it a year or two ago. Thanks again, JB

[IMM]

They are. For the average home a combi is a panacea. Also he is DIYing, where combi's are the by far the easiest solution. A heating and water system in one box. A combi solves many of his immediate and future problems

There is a lot and mostly negative. Stored water is only for large systems, when combi's are not applicable. About 1 million boilers per year are sold in the UK and approaching 70% of them are combi's. They range from the cheap and cheerful basic low flowrates to super sophisticated high flows/high efficiency.

[IMM]

Fitting a modern condensing boiler will drop the gas bill by 40% or so. Your boiler is old and outdated and vastly inefficient. You may as well replace the thing now while you are at it and get a proper up to date system. Using a combi is simplicity in itself. It is not worth nickel & diming it, get rid and do it properly. You will not regret it.

[JB]

Jesus! I had no idea the older ones were as bad as that! Time to talk to a few suppliers I think. thanks again,

JB

[Set Square]

Remember if you *do* go for a new condensing boiler, it doesn't *have* to be a combi - there are plenty of conventional boilers around. If you *do* go combi, you can *still* have stored hot water by using the HW side to heat (say) just the water for the kitchen tap, and use the CH side to heat the radiators *and* the hot water cylinder - using suitable zone valves.

[JB]

I didn't know you could do that! I really must do some research into this. I do want to be able to DIY this retrofit, (except the gas of course), but I want the job to be as straightforward as possible. Cheers, JB

[IMM]

A condensing combi is the easiest, and most cost effective, and will meet your requirements without power showers pumps and all the rest of it.

[Andy Hall]

*If* the mains water supply is adequate and *if* the selected combi meets the hot water production requirements in the bathroom(s) and wherever else hot water is used.

[Set Square]

Whereas a combi may be easier than a conventional boiler to install in a "new build" situation, it certainly isn't so in the case of a replacement.

If there's an existing stored hot water system, a replacement conventional boiler will connect straight to it, in place of the old one. If you install a combi instead, you have to remove, divert, cap, etc. the existing hot water system. Also, hot water *distribution* needs to go via the combi. It's quite possible that the existing hot water distribution pipes don't go anywhere near to the boiler location - requiring a lot of new plumbing.

[IMM]

That has already been emphasised., but thank for your solid contribution.

[IMM]

You must pay attention.

- He needs a new cylinder and all sorts of controls as a bare minimum.

- He now realises his boiler was built by George Stephenson and needs to new one to get the bills down.

- Gas has gone up by 10-12%, and will not go down again.

- He is DIYing too, so his skill level is limited.

- He needs a cost effective, simple system to install that will clear his problems.

- A system that is sound for many years to come.

- A system that is economical to run

In his situation a high flow combi the business.

[Andy Hall]

Cylinders are not expensive and there are system boilers which have almost all of the controls internally

There is a broad range to choose from including combi and non combi.

Which is a reason to buy a condensing boiler of some kind.

That is an incredibly patronising remark. Why do you automatically assume that DIY implies limited knowledge, skill and the wherewithal to do the job?

One option among many others depending on the requirements and the services.

[Set Square]

No, *you* must pay attention!

His boiler is in the garage where there is very *unlikely* to be any hot water distribution - and probably not even a cold mains supply. What could be simpler than slotting in a new conventional boiler, and connecting the flow, return and gas (Corgi permitting!) pipes to it? He would need a *lot* of new pipework to support a combi.

He has said that he wants to replace his hot cylinder. A new one will slot in with more or less the same connections - far more easily than removing it altogether and dealing with the redundant pipes. Inserting a couple of zone valves, or a mid-position valve is hardly rocket science!

True. but *he* didn't say it. Fuel cost was not originally high on his priorities - but now he has been alerted to it, he needs an *efficient* boiler - which doesn't *have* to be - and would probably be better *not* being - a combi.

That's patronising!

Agreed.

No! There are better options, as explained above.

[IMM]

A decent quick recovery coil cylinder is not exactly cheap.

"almost" is the word. He still has to figure out the control wiring, etc. A system boier with all thecontrols internally is pretrty well the same internall as a combi. May as well go for a combi.

You are very good at this are you?

A remark based on experience. DIYers need the simplest system to install, otherwise it becomes a mess.

He obviously has limited knowledge that is why he asked questions here.

The best option for his total circumstances.