Another boiler problem

paul_pockets

Hello, (my first post!)

I have a Ravenheat 820/20, approx 10years old.

I have hot radiators but only warm hot water, although at 7am and 7pm it's really hot? Also if you reduce the water flow through the taps it will run hotter.

I have had a heating engineer replace the divertor value diaphragm. He said the value itself looked good, it made no difference to the hot water. He then removed the heat exchanger and dunked it in some limescale eating stuff. This has made no difference either. (total so far £200)

His next suggestion is to replace the heat exhanger (approx £350 inc labour) or fit a Baxi Platinum 28HE (£2000 inc labour and vat).

I've just spoken to another engineer and he thinks it is the divertor value itself and wants £200 to replace it.

Does anyone have any suggestions as to what would be my best course of action?

I'm a little tuck for £2000 at the moment, but could get it if this is my best long-term course of action.

many thanks
paul

moneysavingplumber

Have you checked the flow-rates at the the different times you've stated? At 7am and 7pm the demand on the water mains will be higher which will mean lower flow rates. There is a screw on the divertor assembly on the newer Ravenheats for reducing the flow rate, I don't know if this is also on the older ones. A flow cup available from plumbers merchants will be able to tell you if the flow rate is set correctly (9-11 litres per minute).

Failing that, it could still be sludge in or near the heating circuit side of the plate heat exchanger.

paul_pockets

Thank for the prompt reply.
I haven't tested the flow during the hot times.

To get hot out of the taps during the day the enginner said it seemed like the flow was approx 3lpm. That isn't acceptable.

Sludge is bad, i'm assuming? Can it be removed?

Would you recommend changing the heat exchanger?

many thanks
paul

moneysavingplumber

It's difficult to say without seeing it what course of action to take. I'm not sure exactly how the gas control valve and burner modulate on this boiler, but that, as well as blocked gas supply, or a faulty gas governor, could also be a factor. A decent engineer should be able to diagnose by elimination on site before committng you to replace any costly parts or replace the boiler.

I'd be looking at examining the water in the system for sludge, checking the gas pressures, burner pressures, fan, flue terminal location, thermal sensors (resistance accross these when cold usually tells if they are faulty or not) in order to narrow down the possibilities, the above checks wouldn't take more than 10 minutes to carry out.

I would call Ravenheat and ask them for the name of their local service agent and have a chat with them and see how much it will cost for them to come out (a call-out charge is likely as with all service-agents) as they are more familiar with the appliance.

caveat_emptor

paul_pockets wrote:

Hello, (my first post!)

I have a Ravenheat 820/20, approx 10years old.

I have hot radiators but only warm hot water, although at 7am and 7pm it's really hot? Also if you reduce the water flow through the taps it will run hotter.

I have had a heating engineer replace the divertor value diaphragm. He said the value itself looked good, it made no difference to the hot water. He then removed the heat exchanger and dunked it in some limescale eating stuff. This has made no difference either. (total so far £200)

His next suggestion is to replace the heat exhanger (approx £350 inc labour) or fit a Baxi Platinum 28HE (£2000 inc labour and vat).

I've just spoken to another engineer and he thinks it is the divertor value itself and wants £200 to replace it.

Does anyone have any suggestions as to what would be my best course of action?

I'm a little tuck for £2000 at the moment, but could get it if this is my best long-term course of action.

many thanks
paul

It is truly amazing how these guys work. You've already paid £200 for diverter valve repair which hasn't improved the situation and someone else wants to do the same job. If there is good DHW flow through the boiler it would suggest that the heat exchanger is ok. If the primary heating side was leaky then your boiler pressure would fall.
Is the burner on full flame or on modulation when the DHW flow is high. Seems that the boiler might be on modulation on all the time for DHW.

moneysavingplumber

It doesn't take alot of sludge in the primary circuit to interfere with heat transfer to DHW, which is why manufacturers invalidate the warranties if they have evidence the system hasn't been correctly flush on installation, and there would not necessarily be a leak on the circuit. Changing the plate HE won't necessarily solve the problem if the overall primary circuit is sludged.

A simple burner-pressure and gas-rate check whilst running the hot tap would reveal if the burner was modulating to CH mode all the time. Any decent fault-finding engineer will keep an open mind whilst carrying out these checks, especially on such a vague problem. Try and find someone familiar with this model that will be happy to carry out a series of diagnostic checks for a reasonable flat fee with no obligation. If it were one of my customers I would be more than happy to do this and would charge no more than the labour charge for the time i spent doing it, probably no more than half an hour.

paul_pockets

that is what i find confusing, that the 2nd guy wants to look at the same thing, although the first man said it was all good. The first guy did say that it might be a good idea to change the whole valve at the same time as the heat exchange unit though.

The first guy just changed the diaphragm, the 2nd guy wants to change the whole thing.

caveat_emptor:
There isn't good DHW apart from at 7am and early evening. the other times you need to turn the flow so low that it is a joke to get piping hot water.

I don't know what 'on modulation' means, sorry. When the hot water is running continuos, the flame is on full, unless the flow is really low then it clicks on and off.

thanks
paul

moneysavingplumber

Well, £200 for a diaphragm repair is a rip-off in my opinion anyway. The other guy is saying it's the divertor because it's the obvious thing to look at, but there are always other, cheaper, possibilities that it would be sensible, and perfectly possible, to eliminate first.

caveat_emptor

paul_pockets wrote:

that is what i find confusing, that the 2nd guy wants to look at the same thing, although the first man said it was all good. The first guy did say that it might be a good idea to change the whole valve at the same time as the heat exchange unit though.

The first guy just changed the diaphragm, the 2nd guy wants to change the whole thing.
caveat_emptor:
There isn't good DHW apart from at 7am and early evening. the other times you need to turn the flow so low that it is a joke to get piping hot water.
I don't know what 'on modulation' means, sorry. When the hot water is running continuos, the flame is on full, unless the flow is really low then it clicks on and off.
thanks
paul

I said good DHW FLOW, not TEMPERATURE, as this would check that the heat exchanger secondary was clear. When the DHW has reached the DHW thermostat temperature the burner should turn down (modulate) to prevent the boiler overheating. You can check this by turning DHW off so the boiler heats the CH on full flame and then turning your DHW on and noting any change in burner. It seems from what you've said that for DHW the burner might be on modulation all the time. When you have good flow the water is cool and when you reduce flow to 3lpm DHW is hot.

paul_pockets

sorry I misunderstood the DHW flow and DHW temp. The flow of water from the hot tap is good, just cold, as you said.

I'll check this when I go home tonight.

If the burner is modulating all the time, what is the solution?

thanks
paul

Fruitcake

On the non technical side, you have paid someone £200 to repair your boiler, yet the problem still persists. This could be construed as a breach of contract under the Supply of Goods and Services Act 1982. It would however depend on what you actually asked them to do.

If you asked them to have a look at your boiler and try to find out what was wrong with it, fair enough they have done this but were unable to fix the problem.

If however you specifically asked them to repair the boiler, they have failed to do this yet still charged you £200. If this is the case they have not met the terms of the contract and you should ask for your money back.

Having had bits replaced one at a time over several visits on my boiler, I do appreciate how difficult troubleshooting can be. However, if you have asked for your boiler to be repaired, you should not be expected to pay until it is. In addition, you should only have to pay for replacing the part that was faulty, not ones that were replaced as part of a process of elimination. Unfortunately this is a grey area as the fault could be caused by several different components where changing all of them cures the problem but not until the last one has been replaced.
The problem then is you don't know if they were all faulty or only the last one without putting the original parts back on and trying the boiler again. Also, you don't know if the repairer has knowingly replaced good items unnecessarily just to get more money out of you. If you suspect this you should ask that you be given the displaced parts, that way they won't get put on someone elses boiler. This particular scam was highlighted on one of the TV programmes a few years ago, possibly "Rogue Traders."

The post suggesting you get a fixed price diagnostic sounds the best to me, then armed with that you should be able to get a better idea of the cost of the repair. Always get a written quote for a specific job, in this case you want to see words like "To repair boiler" or "To remedy low DHW temperature."

Good Luck

Fruitcake

You Only Listen To Me When I'm Wrong