New boiler fitted - unhappy with hot water setup.

[RigidRaider]

I'd appreciate your experienced thoughts on this:

We have a really first class plumber who we trust completely and who has always done excellent work for us over the years. Not the cheapest, but we want a good job done.

Recently he removed the 20 y.o. cast iron boiler, which was leaking like a good 'un and replaced it with a Glow Worm Flexicom 24hx condensing boiler, along with a lot of the major pipework because the house had been plumbed when built with two separate zones and we wanted the boiler moved as well as everything simplified and running off one Y plan valve. The original pipework to the cylinder coil was 22mm but he has replaced it with 15mm plastic while the heating circuits remain 22mm.

It's a detached 4 bed house with 11 rads, well insulated. Traditional open system, fully pumped.

Now we are unhappy aboput the hot water as we don't seem to be getting as much as before. This week the heating has come on again and the problem seems even worse - we never had any shortage before but now we've had a couple of cool showers. We have not changed the timings of the CH or HW and all the stats and controls are new, with the exception of the cyclinder stat, which is a year old. It seems to work OK, clicking when you turn the wheel through the expected temperature and the boiler reacts correctly. The plumber has already been back and fitted an automatic air bleed on the vertical branch off the cyclinder coil (just a tap bleed before) and while he was doing this he got a lot of air out of the circuit. It is certainly a lot better now but still we are concerned.

I have two questions:

1 - Is a Flexicom24 adequate for this house? He tells me it's 80,000 BTU and it is the right size.

2 - It it right to have only 15mm pipework to the HW coil while the CH pipework out of the Y valve is 22mm? Wouldn't this create an imbalance in the distribution of hot water through the valve?

The (new) circulating pump is running on fast speed btw.

 

[bengasman]

Sounds like your timer is not set right, or you don't have independent timing.
Boiler is easily big enough, unless you have extremely large rads; look in faq if you want to know the capacity of the existing rads.

Systems with a cylinder should have completely separate times for heating and hot water production; if they are both on at the same time, both sides will be slow to respond.
Unless you have an uneconomically oversized boiler.

 

[fatplumber]

I don't like the use of plastic but the sizing shouldn't be an issue.

 

[RigidRaider]

Thanks - both replies make me feel better and yes, I agree about giving the boiler too much work. We'll re-time the water to come on an hour before the CH.

 

[gas4you]

Is there a balancing valve fitted to the 15mm plastic on the return from the cylinder? I wouldn't have thought so with 15mm, but if there is check it is fully open.

 

[Agile]

My first reaction is that whilst you like your plumber's work you dont seem to perceive him as an expert and think that you know more about the industry than he does.

I reach this conclusion because the house probably needs TWO heating zones under the energy efficiency regulations yet you overuled him and insisted that he removes the two zone system.

When fitting a new boiler, the recommendation is that the cylinder is replaced with a modern fast reheat model at the same time. The output temperature of a modern boiler ( 70° ) is lower than your old boiler ( 80° ) and that will also have the effect of increasing the already slow reheat time of your old cylinder.

The 15 mm supply to the cylinder is probably adequate but that depends on the length which has not been stated. However, when reheating you could measure or feel the flow and return at the cylinder. It should be a maximum of 20° difference. That will be very efficient but will result in a longer reheat than before when the differential was a design target of 11°.

The motto is that you should employ a heating expert to design your system instead of making those decisions yourself. Whilst your plumber may do good and cheap work, he does not seem to me to have much of an idea about heating design particularly when he allows your two zones to be removed and when you have ask about your system on this forum.

Tony Glazier

 

[fekarrs]

Blimey, Tone's on his soap box again!

Trust his advice, but don't let the stern lecture get to you.

You're not the first
//www.diynot.com/forums/viewtopic.php?p=1239928#1239928

And you won't be the last. Still, as long as he's happy.

 

[RigidRaider]

Thanks for the lecture! I don't pretend to know anything at all about the plumbing industry but what I do know is that, as Le Corbusier said, a house should be a machine for living in and this house wasn't. The house was built 20 years ago by a bloke who has a reputation locally for thrift and had unusual ideas about how to plumb and wire a house. The upstairs zone was controlled by a simple switch, which enabled him to warm the upstairs rads for a few minutes before the wife and kids went to bed. As a concession to comfort though he did put the bathroom rad on the HW circuit so it warmed up after you'd drawn water. At that time the philosophy seemed to be to hide the motorised valves in the floor voids and at the side of the airing cupboard where they couldn't be reached. Since we bought the house both have malfunctioned and we have grown tired of messing around, trying to get the system working properly so when the new boiler came we opted to have both upstairs and downstairs heated simultaneously and controlled by one Y valve in an easily accessible place on the utility wall where it can be serviced in future years. We didn't over-rule the plumber or insist, we merely suggested and he agreed. If we had had more cash I expect we could have gone deeper into the heating and HW system and upgraded the cylinder as you suggest but the alarming amount of water seeping from the seams on the heat exchanger of the old boiler made replacement a bit urgent. It wasn't undertaken lightly though as we had to sell our cherished 1986 ex-MOD Land Rover 90 to fund it.

We did get a decent electrician specialising in heating and boilers to upgrade all the controls.

The plumber we use is not cheap by any means; I've no doubt we could have found cheaper but his blokes come at 8.30 on the appointed day, don't chat and mess around, are clean, tidy and hard working and don't smell of booze on Monday mornings. Above all we pay craftsmen like this plumber extremely promptly because we believe that if you treat your suppliers well they will reciprocate by giving you excellent service. This plumber certainly drives the 20 miles over to see us if we ask him to come, without question. This is very valuable when you are married to a woman who is permanently cold.

By the way the wife of the bloke who built the house walked out on him 5 years ago taking the kids with her!

I am grateful for your advice on flow and return temps because I'm interested in getting this boiler working at its best so will try to find a way of monitoring them. Anybody got any suggestions?

 

[fekarrs]

When the Great Tony one has climbed down from his ivory tower, he may deign to offer you the benefit of his knowledge. All hail!

 

[Agile]

It seems a little odd to me that the "plumber" apparently does not have the ability or his own electrician to wire up the heating controls.

It also seems that not only did he not advise you that two zones were necessary or probably that all ( or at least bedroom ) rads should be fitted with TRVs.

I do realise that customers are more interested in people coming at previously arranged times rather than getting the best technical advice. I am also aware that although I give the best technical advice it does not make everyone happy either.

Tony

 

[RigidRaider]

I fitted TRVs to all the rads except for one on each floor a couple of years ago.

The plumber admitted that he doesn't do any more than simple electrics and I'd do better to call a heating controls specialist. The changes to the controls were complete, everything was re-done from fresh. Both the plumber and the sparks suggested we might want to keep the two zones but we were strongly against the idea, my wife because she likes the whole house to be warm and I because my belief is that you heat not only the air in the house but the structure of the house, internal walls, fittings, furniture etc and there's no point in doing this unevenly. A well insulated house (as is ours) should form a large cubic (if possible) mass of uniformly warm material to be comfortable and efficient.

I have borrowed a couple of pipe thermometers from my neighbour and can now see that when the boiler is firing the F & R pipes are running at around 10 degrees difference.

What is your opinion on the correct location for the cyclinder 'stat? Somebody told me that I should move it to near the bottom of the cylinder in order to achieve a biger usable volume of hot water but thinking about this I can see that if you put it near the bottom level of the coil you'd be forcing the boiler to flog itself ad infinitum as the heat gradient would never reach that far down. The traditional one third up the cylinder would seem to be the place where the stat would register the bottom of the zone of usable hot water.

 

[Agile]

I understand your feelings about zoning but there are the Building regulations which we are expected to follow and subsequent owners might be more concerned about keeping heating costs to a minimum.

A 10° differential on the heating coil indicates that the 15 mm feed pipes are not too small and indeed the flow rate is a bit too high to enable the most efficient boiler operation.

The stat position is usually best at about the position of the top of the heating coil if that is lower than 1/3 of the way down.

Putting it lower is going to mean much longer heating times and inefficient heat transfer.

You should time your hot water reheat to be reheating immediately hot water is used, to minimise recovery time ( as well as ensuring its fully heated by the time the first use takes place ).

Tony

 

[RigidRaider]

Thanks again.

Last night I turned the circulator speed down from 111 to 11. I reckon you can circulate the water too fast for useful heat transfer at both ends. I'm watching it with interest. What would be the ideal difference, around 11 degrees as you wrote earlier?

Have you the time to summarise these regs on zoning briefly for me? I remember inspecting the installation in a Hungarian freind's new house and being impressed with the array of pumps and controllers for several zones in the house.

 

[gas4you]

Thanks again.

Last night I turned the circulator speed down from 111 to 11. I reckon you can circulate the water too fast for useful heat transfer at both ends.

Yes you are correct. The example I always give is that of a kettle with the lid off, placed under a cold tap and switched on.

If the cold tap is running too fast, then kettle will never heat up/boil the water properly.

 

[Agile]

The pump is usually best on setting "2" if everything is properly designed and fitted.

You will have a condensing boiler and they are most efficient with a differential of about 20°. It does depend on the model and the manufacturers recommendations. Most are not too bad down to 15° but I would recommend trying to achieve that if possible.

A properly designed system will have a gate valve on the cylinder heating coil to enable the flow rate to be set to the optimum. It can vary a bit depending on whether the heating is on or not. If an auto bypass valve is fitted then they can be carefully adjusted to keep it pretty constant but few installers bother about anything that advanced.

If you have lowered your pump setting then you should remeasure the heating coil differential when it is reheating from cold rather than nearly finished.

A property needs two ( or more ) seperately controlled heating zones if the floor area exceeds 150m².

Tony