Vokera hot water temp problems

[Shaun71]

My boiler is a Vokera Excell 80SP

When running a bath, the temp on the boiler gets to about 60 degrees then cuts the boiler out. Cold water is then pulled through the taps. It then builds back up to temp before doing the same leaving a luke warm bath.

Insurance people came out and changed the thermistor and still the same. They now recommend a power flush to hopefully solve the problem. Quoted £450 + VAT. Got a second quote of a local Corgi registered plumber of £200 + VAT but without no guarantee of working.

I know its a seperate circuit but I have just removed all the homes rads and flushed them all out. I expected the water to be dirty but not at all.

Is there any effective way I can flush the secondary heat exchanger myself?

 

[Agile]

It may still be blocked but the diagnosis involves measuring temperatures within the boiler with a digital contact thermometer.

Its a relatively easy job for a professional but not one I would recommend for a first timer on that model. Depends on your abilities.

Tony

 

[Shaun71]

OK cheers.

A friend (Corgi registered plumber) has mentioned he will have a look at it. Is removing the H/ex and cleaning it a major operation?

Would putting one of the various 'anti sludge' solutions in the system help?

 

[DIY_MAD]

Shaun

I had the exact same problem on my 80SP last month. It also appeared that the burners were been blown out.

I got BG out on a service contract to come and fix it. They changed the gas diverter valve, cleaned the fan in the flue and gave it a good service. The thermistor was changed previous and didn't resolve the problem

All is well now. plenty of hot water at a good preasure.

 

[DIY_MAD]

Shaun

Try running the water while the heating system is hot. I found that the problem wasn't as bag when it was on. Then the heating was off the water fluctuated from hot to stone cold.

 

[Shaun71]

Im also with British Gas as well, paying £12 a month (cant remember what the tariff is called)

Ive only been with them a month or so and they gave it a clean bill of health in their initial safety check, now all this is happening.

Might give them a bell and get them to have alook at it. Like I said Ive drained all the rads and the water is clean as a bell. i know its a different circuit but I thought it would give me some idea if there was sludge in the system

 

[Shaun71]

DIY_MAD

Cheers, my boiler just seems to cut off though. The burners dont seem to blow out.

Its a bit better when you run it slowly as theres less cold water being pulled through.

 

[DIY_MAD]

As you say its a different circuit. I don't think the heating should effect the HW.

I found BG to be very helpful. I called them at 7.30pm on Monday and they turned up on time on Tuesday afternoon. I cannot fault service like that. (No I don't work for BG or have anything to do with them)

 

[phil bancroft]

heating works but no hot water, try hitting the pressure differential switch with your slipper with the hot water tap on (top right of the boiler unit) if this works you need another switch, cost about £40

 

[croydoncorgi]

You're paying British Gas for 'service' (in both senses!). Why not make them fix it? Ok - they may quickly give up and say the boiler is 'beyond economic repair' but that's a different issue. If you then find that the 'service' is unsatisfactory, change to another supplier.

(You may gather from this that I'm a BG competitor! I prefer to keep the playing field level.)

 

[DP]

They changed the gas diverter valve, cleaned the fan in the flue and gave it a good service. The thermistor was changed previous and didn't resolve the prob.

What is a gas diverter valve? I regularly work on this model of boiler but have never come across a gas diverter valve.

Try running the water while the heating system is hot. I found that the problem wasn't as bag when it was on. Then the heating was off the water fluctuated from hot to stone cold.

During heating mode, no water should go to the radiators. If it is above could be true but the function will be eroneous. Combi boiler can ONLY heat rads OR hot water at any one time.

During heating mode the main heat exchanger heats the system water and pump propels water to the radiators. Heat generated at the heat exchanger is 'soaked up' by the radiators. If the heat generated by the heat exchanger is greater than that set on CH thermostat on front panel, flame size is reduced.

During HW mode NO water goes to the rads. The heated water circulates within the boiler. This heat is removed at the water to water heat exchanger (HW heat exchanger). Combi boiler is designed to transfer all the heat generated to the cold water that you would find hot at the tap.

If heat generated by the main heat exchanger is slightly greater than what the HW HE can use, main burner will downsize. Result is near constant HW delivery. If the heat generated by main HE is greater than can be used by HW HE (like if flow of water through the HW HE is reduced due to sedimental blockage) burner will not downsize (this stage will be bypassed) but will shut down. This allows the primary water (one that flow through main heat exchanger) to cool down. Thermistor 'sees' all this and fires the burners to maintain safe operation.

Clean water does not mean you do not have a problem. In system plumbed with plsatic pipe, you can have scale that does not colour the water but blockage can be total. Am working on a systen where I had to replace all the plastic pipes. A six foot section has 40 bars of pressure applied to it. Water oozed from the end but failed to clear the blockage. Water was clear.